Word problems with Linear and Quadratic Equations

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Word problems with Linear and Quadratic Equations
Prepared by Doron Shahar Chapter 1 Section 1.2 & 1.5 Word problems with Linear and Quadratic Equations

Warm-up Write each description as a mathematical statement.
Prepared by Doron Shahar Warm-up Write each description as a mathematical statement. Page 9 #1, 3 more than twice a number Page 9 #2, The sum of a number and 16 is three times the number. 1.2.1 The sum of three consecutive integers is What is the smallest of the three integers? 1.5.1 The sum of the square of a number and the square of 7 more than the number is 169. What is the number?

Page 9 #1 Variable: Let x be the number. Expression:
Prepared by Doron Shahar Page 9 #1 Write “3 more than twice a number” as a mathematical statement. Variable: Let x be the number. Expression:

Page 9 #2 Variable: Let x be the number. Equation:
Prepared by Doron Shahar Page 9 #2 Write “the sum of a number and 16 is three times the number” as a mathematical statement. Variable: Let x be the number. Equation:

1.2.1 Want: The smallest of the three integers. Variable:
Prepared by Doron Shahar 1.2.1 The sum of three consecutive integers is 78. What is the smallest of the three integers? Want: The smallest of the three integers. Variable: Let x be the smallest of the three integers. Examples of consecutive integers: 1, 2, 3 17, 18 ,19 25, 26, 27 x, x+1, x+2 Equation:

1.5.1 Want: The number. Variable: Let x be the number. Equation:
Prepared by Doron Shahar 1.5.1 The sum of the square of a number and the square of 7 more than the number is 169. What is the number? Want: The number. Variable: Let x be the number. Equation:

Approach to word problems
Prepared by Doron Shahar Approach to word problems Solving word problems involves two key steps: Constructing the equations you are to solve. Solving the equations you found. The word problems in sections 1.2 and 1.5 will lead to linear and quadratic equations, which we have just learned how to solve. Therefore, we shall not solve any of the word problems in class. Rather we will focus on constructing the equations. That is, we will translate the word problems into equations.

1.5.2 Projectile Problem Want:
Prepared by Doron Shahar 1.5.2 Projectile Problem A stone is thrown downward from a height of meters . The stone will travel a distance of s meters in t seconds, where s=4.9t2 +49t. How long will it take the stone to hit the ground? Want: The time it will take the stone to hit the ground. Variable: Let T seconds be the time it will take the stone to hit the ground. Equation: To find the equation, let’s try using a picture.

Prepared by Doron Shahar
1.5.2 Equation T is the time it will take until the stone hits the ground. Initial Height Distance traveled in T seconds 4.9T2+49T meters 274.4 meters Equation:

1.5.2 Summary It will take 4 seconds for the stone to hit the ground.
Prepared by Doron Shahar 1.5.2 Summary Want: The time it will take the stone to hit the ground. Variables: Let T seconds be the time until the stone hits the ground. Equation: Solutions to equation: Note that T=−14 cannot be the answer to the word problem, because T denotes the time it will take the stone to hit the ground. So T>0. Solution to word problem: It will take 4 seconds for the stone to hit the ground.

Extra Projectile Problem
Prepared by Doron Shahar Extra Projectile Problem A cannonball is launched from a cannon. The height, h, in feet of the cannonball t seconds after it leaves the cannon is given by the equation h=−16t2+63t+4. When will the cannon ball hit the ground? Want: The time when the cannonball hits the ground. Variable: Let T seconds be the time from when the cannonball is launched until it hits the ground. Equation: To find the equation, let’s try using a picture.

Extra problem: Equation
Prepared by Doron Shahar Extra problem: Equation The height, h, in feet of the cannonball t seconds after it leaves the cannon is given by the equation h=−16t2+63t+4. T is the time when the cannonball hits the ground. After T seconds, the cannonball is on the ground, and has a height of 0 feet. Equation:

Extra problem: Summary
Prepared by Doron Shahar Extra problem: Summary Want: The time when the cannonball hits the ground. Variables: Let T seconds be the time from the cannonball is launched until it hits the ground. Equation: Solutions to equation: Note that T=− cannot be the answer to the word problem, because T denotes the time until the cannonball hits the ground. So T>0. Solution to word problem: The cannonball will hit the ground about 4 seconds after it was launched.

1.5.4 Geometry Problem Want: Length of the side of the square
Prepared by Doron Shahar 1.5.4 Geometry Problem The area of a square is numerically 60 more than the perimeter. Determine the length of the side of the square. Want: Length of the side of the square Variables: Let S be the length of the side of the square. Let A be the area of the square. Let P be the perimeter of the square. Equations: Information given in the problem. Facts from geometry

1.5.4 Equations Want: Length of the side of the square Key Variable:
Prepared by Doron Shahar 1.5.4 Equations Want: Length of the side of the square Key Variable: Let S be the length of the side of the square. Equations: What method can we use to solve for S given these equations? Substitution Now solve for S.

1.5.4 Summary The side of the square is 10 units long. Want:
Prepared by Doron Shahar 1.5.4 Summary Want: Length of the side of the square Key Variable: Let S be the length of the side of the square. Key Equation: Solutions to equation: Note that S=−6 cannot be the answer to the word problem, because S denotes the length of the side of the square. So S>0. Solution to word problem: The side of the square is 10 units long.

1.5.5 Geometry Problem Want: Length and Width of the rectangle
Prepared by Doron Shahar 1.5.5 Geometry Problem The length of a rectangle is 7 centimeters longer than the width. If the diagonal of the rectangle is 17 centimeters, determine the length and width. Want: Length and Width of the rectangle Variables: Let L cm be the length of the rectangle. Let W cm be the width of the rectangle. Let D cm be the perimeter of the square. Equations: Information given in the problem. Fact from geometry

1.5.5 Equations Want: Length and width of rectangle
Prepared by Doron Shahar 1.5.5 Equations Want: Length and width of rectangle Let L cm be the length of the rectangle. Key Variables: Let W cm be the width of the rectangle. Equations: What method can we use to solve for L and W given these equations? Substitution Now solve for W. Then solve for L.

1.5.5 Summary The width of the rectangle is 8 cm.
Prepared by Doron Shahar 1.5.5 Summary Want: Length and width of rectangle Let L cm be the length of the rectangle. Key Variable: Let W cm be the width of the rectangle. Key Equations: Solutions to first equation: Note that W=−15 cannot be the answer to the word problem, because W denotes the widths of the rectangle. So W>0. Solution to word problem: The width of the rectangle is 8 cm. The length of the rectangle is 15 cm.

Key Idea for many word problems
Prepared by Doron Shahar Key Idea for many word problems In the previous problems, the equations we are trying to find are almost given, or else come from basic facts about geometry. Next we will have to find the equations.

Key Idea for many word problems
Prepared by Doron Shahar Key Idea for many word problems Once we have an equation of the form, We may need to use formulas to replace the amount when dealing with values and costs.

1.2.2 General problem Well, it depends on how many coins she
Prepared by Doron Shahar 1.2.2 General problem Tina has \$6.30 in nickels and quarters in her coin purse. She has a total of 54 coins. How many of each coin does she have? Well, it depends on how many coins she has that are not in her coin purse. Want: The number of nickels and the number of quarters. Variables: Let N be the number of nickels. Let Q be the number of quarters.

1.2.2 Equations What is the amount being added? Number of coins Number
Prepared by Doron Shahar 1.2.2 Equations What is the amount being added? Number of coins Number of nickels Number of quarters Total Number of coins Dollar Value Dollar Value of nickels Dollar Value of quarters Dollar Value of all coins

1.2.2 Summary Want: The number of nickels and the number of quarters.
Prepared by Doron Shahar 1.2.2 Summary Tina has \$6.30 in nickels and quarters in her coin purse. She has a total of 54 coins. How many of each coin does she have? Want: The number of nickels and the number of quarters. Variables: Let N be the number of nickels. Let Q be the number of quarters. Equations: What method might we use to solve this system of equations? Elimination

Prepared by Doron Shahar
1.2.3 General problem A company produces a pair of skates for \$43.53 and sells a pair for \$ If the fixed costs are \$742.72, how may pairs must the company produce and sell in order to break even? Want: The number of pairs of skates that must be produced to break even. Variables: Let S be the number of pairs of skates that must be produced to break even.

1.2.3 Equation Rent What is the amount being added? Fixed costs
Prepared by Doron Shahar 1.2.3 Equation Fixed costs Break even Rent Money Earned = Total Cost What is the amount being added? Cost Fixed Cost Production Cost Total Cost

Prepared by Doron Shahar
1.2.3 Summary A company produces a pair of skates for \$43.53 and sells a pair for \$ If the fixed costs are \$742.72, how may pairs must the company produce and sell in order to break even? Want: The number of pairs of skates that must be produced to break even. Variables: Let S be the number of pairs of skates that must be produced to break even. Equation:

Prepared by Doron Shahar
Warm-up Page 9, How much pure salt is in 5 gallons of a 20% salt solution? Page 20 #3, An alloy contains 40% gold. Represent the number of grams of gold present in G grams of the alloy. Page 9, What is the equation involving distance, rate, and time? Page 20 #1, A car is travelling M mph for H hours. Represent the number of miles traveled.

Key Idea for many word problems
Prepared by Doron Shahar Key Idea for many word problems In the previous problems, the equations we are trying to find are almost given, or else come from basic facts about geometry. Next we will have to find the equations.

Key Idea for many word problems
Prepared by Doron Shahar Key Idea for many word problems Once we have an equation of the form, We may need to use formulas to replace the amount when dealing with percents and rates.

Key Idea for mixture problems
Prepared by Doron Shahar Key Idea for mixture problems Below is the formula for percents. Page 9, How much pure salt is in 5 gallons of a 20% salt solution?

Key Idea for mixture problems
Prepared by Doron Shahar Key Idea for mixture problems Below is the formula for percents. Page 20 #3, An alloy contains 40% gold. Represent the number of grams of gold present in G grams of the alloy.

1.2.4 Mixture problem Want: The number of pounds of almonds she added.
Prepared by Doron Shahar 1.2.4 Mixture problem A premium mix of nuts costs \$12.99 per pound, while almonds cost \$6.99 per pound. A shop owner adds almonds into the premium mix to get 90 pounds of nuts that cost \$10.99 per pound. How many pounds of almonds did she add? Want: The number of pounds of almonds she added. Variables: Let A be the number of pounds of almonds she added. Let P be the number of pounds of the premium mix of nuts.

1.2.4 Equations What is the amount being added? Mass (Pounds)
Prepared by Doron Shahar 1.2.4 Equations What is the amount being added? Mass (Pounds) Pounds of almonds Pounds of premium mix Total Pounds in mixture Cost Cost of almonds Cost of premium mix Total cost of mixture

1.2.4 Summary Want: The number of pounds of almonds she added.
Prepared by Doron Shahar 1.2.4 Summary A premium mix of nuts costs \$12.99 per pound, while almonds cost \$6.99 per pound. A shop owner adds almonds into the premium mix to get 90 pounds of nuts that cost \$10.99 per pound. How many pounds of almonds did she add? Want: The number of pounds of almonds she added. Key Variable: Let A be the number of pounds of almonds. Equations: What method might we use to solve this system of equations? Elimination

Prepared by Doron Shahar
1.2.5 Mixture problem A chemist wants to strengthen her 40L stock of 10% acid solution to 20%. How much 24% solution does she have to add to the 40L of 10% solution in order to obtain a mixture that is 20% acid? Want: The volume of the 24% solution that the chemist needs to add to obtain a mixture that is 20% acid. Variable: Let V liters be the volume of the 24% solution that needs to be added.

1.2.5 Equation What is the amount being added? (40+V) liters
Prepared by Doron Shahar 1.2.5 Equation (40+V) liters of solution 40 liters of solution V liters of solution 20% acid 10% acid 24% acid Beaker 3 Beaker 1 Beaker 2 What is the amount being added? Volume of acid Volume of acid in beaker 1 Volume of acid in beaker 2 Total volume of acid in beaker 3

Prepared by Doron Shahar
1.2.5 Summary A chemist wants to strengthen her 40L stock of 10% acid solution to 20%. How much 24% solution does she have to add to the 40L of 10% solution in order to obtain a mixture that is 20% acid? Want: The volume of the 24% solution that the chemist needs to add to obtain a mixture that is 20% acid. Variable: Let V liters be the volume of the 24% solution that needs to be added. Equation:

Key Idea for rate problems
Prepared by Doron Shahar Key Idea for rate problems Below is the formula for rates. Page 20 #1, A car is travelling M mph for H hours. Represent the number of miles traveled.

1.2.7 Distance-Rate-Time Want: The time when they will meet. Variable:
Prepared by Doron Shahar 1.2.7 Distance-Rate-Time Two motorcycles travel towards each other from Chicago and Indianapolis (350km apart). One is travelling 110 km/hr, the other 90 km/hr. If they started at the same time, when will they meet? Want: The time when they will meet. Variable: Let T hours be the time from when they started until they meet.

1.2.7 Equation What is the amount being added? 90 km/hr 110 km/hr
Prepared by Doron Shahar 1.2.7 Equation 90 km/hr 110 km/hr Distance traveled by Motorcycle 1 Distance traveled by Motorcycle 2 Chicago Indianapolis Motorcycle 1 Motorcycle 2 350 km Where they meet What is the amount being added? Distance Distance traveled by motorcycle 1 Distance traveled by motorcycle 2 Total distance traveled by both

1.2.7 Summary Want: The time when they will meet. Variable:
Prepared by Doron Shahar 1.2.7 Summary Two motorcycles travel towards each other from Chicago and Indianapolis (about 350km apart). One is travelling 110 km/hr, the other 90 km/hr. If they started at the same time, when will they meet? Want: The time when they will meet. Variable: Let T hours be the time from when they started until they meet. Equation:

1.5.3 Distance-Rate-Time Want: The speed of Amy’s car. Variables:
Prepared by Doron Shahar 1.5.3 Distance-Rate-Time Amy travels 450 miles in her car at a certain speed. If the car had gone 15 mph faster, the trip would have taken 1 hour less. Determine the speed of Amy’s car. Want: The speed of Amy’s car. Variables: Let A mph be the speed of Amy’s car. Let T hours by the time it takes Amy to drive 450 miles.

1.5.3 Equations A mph for T hours Amy’s car 450 miles (A+15) mph
Prepared by Doron Shahar 1.5.3 Equations A mph for T hours Amy’s car 450 miles (A+15) mph for (T-1) hours Amy’s car 450 miles

1.5.3 Summary Want: The speed of Amy’s car. Key Variable:
Prepared by Doron Shahar 1.5.3 Summary Amy travels 450 miles in her car at a certain speed. If the car had gone 15 mph faster, the trip would have taken 1 hour less. Determine the speed of Amy’s car. Want: The speed of Amy’s car. Key Variable: Let A mph be the speed of Amy’s car. Equations: What method might we use to solve this system of equations? Substitution

1.2.9 Shared Work Problem Want:
Prepared by Doron Shahar 1.2.9 Shared Work Problem Suppose a journeyman and apprentice are working on making cabinets. The journeyman is twice as fast as his apprentice. If they complete one cabinet in 14 hours, how many hours does it take for the journeyman working alone to make one cabinet? Want: The time it takes the journeyman working alone to make one cabinet. Variables: Let J hours be the time it takes the journeyman to make one cabinet working alone. Let A hours be the time it takes the apprentice to make one cabinet working alone.

1.2.9 Equations The journeyman is twice as fast as his apprentice.
Prepared by Doron Shahar 1.2.9 Equations The journeyman is twice as fast as his apprentice. Journeyman’s rate 2 × Apprentice’s rate Multiply both sides of the equation by AJ

1.2.9 Equations What is the amount being added?
Prepared by Doron Shahar 1.2.9 Equations Amount of the cabinet built What is the amount being added? The answer is NOT time!! Amount of the cabinet built by the apprentice in 14 hours Amount of the cabinet built by both in 14 hours Amount of the cabinet built by the journeyman in 14 hours

Prepared by Doron Shahar
1.2.9 Summary Want: The time it takes the journeyman working alone to make one cabinet. Key Variable: Let J be the time it takes the journeyman to make one cabinet working along. Equations: What method might we use to solve this system of equations? Substitution

1.5.6 Shared Work Problem Want:
Prepared by Doron Shahar 1.5.6 Shared Work Problem It take Julia 16 minutes longer to chop vegetables than it takes Bob. Working together, they are able to chop the vegetables in 15 minutes. How long will it take each of them if they work by themselves? Want: The time it takes each of them working alone to chop the vegetables. Variables: Let J minutes be the time it takes Julia to chop the vegetables working alone. Let B minutes be the time it takes Bob to chop the vegetables working alone.

1.5.6 Equations What is the amount being added?
Prepared by Doron Shahar 1.5.6 Equations It take Julia 16 minutes longer to chop the vegetables than it takes Bob. Amount of vegetables chopped What is the amount being added? The answer is NOT time!! Amount of the vegetables chopped by Julia in 15 minutes Amount of the vegetables chopped by Bob in 15 minutes Amount of the vegetables chopped by both in 15 minutes

Prepared by Doron Shahar
1.5.6 Summary Want: The time it takes each of them working alone to chop the vegetables. Variables: Let J minutes be the time it takes Julia to chop the vegetables working alone. Let B minutes be the time it takes Bob to chop the vegetables working alone. Equations: What method might we use to solve this system of equations? Substitution

1.2.8 Shared Work Problem Want:
Prepared by Doron Shahar 1.2.8 Shared Work Problem Suppose it takes Mike 3 hours to grade one set of homework and it takes Jenny 2 hours to grade one set of homework. If they grade together, how long will it take to grade one set of homework? Want: The time it will take them to grade one set of homework if they work together. Variables: Let T hours be the time it will take them to grade one set of homework if they work together.

1.2.8 Equations What is the amount being added?
Prepared by Doron Shahar 1.2.8 Equations Amount of the homework set graded What is the amount being added? The answer is NOT time!! Amount of the homework set graded by both in T hours Amount of the homework set graded by Mike in T hours Amount of the homework set graded by Jenny in T hours

Prepared by Doron Shahar
1.2.8 Summary Suppose it takes Mike 3 hours to grade one set of homework and it takes Jenny 2 hours to grade one set of homework. If they grade together, how long will it take to grade one set of homework? Want: The time it will take them to grade one set of homework if they work together. Variables: Let T be the time it will take them to grade one set of homework if they work together. Equation:

Key Idea for relative motion problems
Prepared by Doron Shahar Key Idea for relative motion problems Downstream Upstream Directions of Boats B mph B mph Direction of Current C mph The boat’s speed going downstream is going upstream is

1.2.6 Relative Motion Problem
Prepared by Doron Shahar 1.2.6 Relative Motion Problem A boat travels down a river with a current. Travelling with the current, a trip of 66 miles takes 3 hours while the return trip travelling against the current takes 4 hours. How fast is the current? Want: The speed of the current. Variables: Let C mph be the speed of the current. Let B mph be the speed of the boat in still water.

1.2.6 Equations For 3 hours B mph C mph 66 miles For 4 hours B mph
Prepared by Doron Shahar 1.2.6 Equations For 3 hours B mph C mph 66 miles For 4 hours B mph C mph

1.2.6 Summary Want: The speed of the current. Key Variable:
Prepared by Doron Shahar 1.2.6 Summary A boat travels down a river with a current. Travelling with the current, a trip of 66 miles takes 3 hours while the return trip travelling against the current takes 4 hours. How fast is the current? Want: The speed of the current. Key Variable: Let C mph be the speed of the current. Equations: What method might we use to solve this system of equations? Elimination

Prepared by Doron Shahar
1.5.7 Relative Motion Maria traveled upstream along a river in a boat a distance of 39 miles and the came right back. If the speed of the current was 1.3 mph and the total trip took 16 hours, determine the speed of the boat relative to the water. Want: The speed of the boat relative to the water. Variables: Let B mph be the speed of the boat relative to the water. Let T hours be the time of the trip upstream.

1.2.6 Equations For T hours B mph 1.3 mph 39 miles B mph
Prepared by Doron Shahar 1.2.6 Equations For T hours B mph 1.3 mph 39 miles B mph For 16−T hours 1.3 mph

1.5.7 Summary Want: The speed of the boat relative to the water.
Prepared by Doron Shahar 1.5.7 Summary Maria traveled upstream along a river in a boat a distance of 39 miles and the came right back. If the speed of the current was 1.3 mph and the total trip took 16 hours, determine the speed of the boat relative to the water. Want: The speed of the boat relative to the water. Key Variable: Let B mph be the relative speed of the boat. Equations: What method might we use to solve this system of equations? Substitution or Elimination

Review of Word Problems
Prepared by Doron Shahar Review of Word Problems Don’t forget units Sanity checks: Check that your answer makes sense Examples: Lengths, times, and speeds should not be negative. If Michael and Rachel can each build a bookcase working alone in under a day, it should not take them more than a day to build a bookcase working together.   If people do not believe that mathematics is simple, it is only because they do not realize how complicated life is.—John Louis von Neumann