# Copyright 2013, 2010, 2007, Pearson, Education, Inc. Section 1.3 Problem Solving.

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Copyright 2013, 2010, 2007, Pearson, Education, Inc. Section 1.3 Problem Solving

Copyright 2013, 2010, 2007, Pearson, Education, Inc. What You Will Learn Problem-solving techniques 1.3-2

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Polya’s Procedure George Polya (1887-1985), a mathematician who was educated in Europe and taught at Stanford, developed a general procedure for solving problems. 1.3-3

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Guidelines for Problem Solving 1. Understand the Problem. 2. Devise a Plan to Solve the Problem. 3. Carry Out the Plan. 4. Check the Results. 1.3-4

Copyright 2013, 2010, 2007, Pearson, Education, Inc. 1. Understand the Problem. Read the problem carefully at least twice. Try to make a sketch of the problem. Label the information given. Make a list of the given facts that are pertinent to the problem. Determine if you have sufficient information to solve the problem. 1.3-5

Copyright 2013, 2010, 2007, Pearson, Education, Inc. 2. Devise a Plan to Solve the Problem. Can you relate this problem to a previous problem that you’ve worked before? Can you express the problem in terms of an algebraic equation? Look for patterns or relationships. Can you express the problem more simply? 1.3-6

Copyright 2013, 2010, 2007, Pearson, Education, Inc. 2. Devise a Plan to Solve the Problem. Can you substitute smaller or simpler numbers to make the problem more understandable? Will listing the information in a table help in solving the problem? Can you make an educated guess at the solution? You can work backward to determine the correct procedure. 1.3-7

Copyright 2013, 2010, 2007, Pearson, Education, Inc. 3. Carrying Out the Plan. Use the plan you devised in step 2 to solve the problem. 1.3-8

Copyright 2013, 2010, 2007, Pearson, Education, Inc. 4. Check the Results. Ask yourself, “Does the answer make sense?” and “Is it reasonable?” If the answer is not reasonable, recheck your method for solving the problem and your calculations. Can you check the solution using the original statement? Is there an alternative method to arrive at the same conclusion? Can the results of this problem be used to solve other problems? 1.3-9

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Example 2: Shuttle Revenue Airport Express shuttle service provides service from San Antonio International Airport to downtown hotels, approximately 10 miles away. One particular shuttle makes 16 round trips per day, carrying 5 passengers per trip. The fare each way is \$18. What are the receipts from one day’s operation for this particular shuttle? 1.3-10

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Solution List all the information: Distance from airport to downtown hotels ≈ 10 miles * Number of round trips per day = 16 * Number of passengers per trip = 5 * Fare each way = \$18 We need only the information with a *. Example 2: Shuttle Revenue 1.3-11

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Solution Round trip costs 2  \$18 = \$36 The total receipts for one day is the product of the number of round trips, the number of passengers, and the cost per round trip = 16  5  \$36 = \$2880 Example 2: Shuttle Revenue 1.3-12

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Example 3: Retirement It is never too early to start planning for retirement. U.S. Census Bureau data indicate that at age 65 the average woman will live another 20 years and the average man will live another 17.2 years. The data also indicate that about 33% of the average person’s retirement income will come from Social Security. 1.3-13

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Example 3: Retirement When discussing retirement planning, many investment firms and financial planners use the graph in the figure on the next slide which shows how long a typical retiree’s assets (or “nest egg”) will last based on the percentage of the assets withdrawn each year. 1.3-14

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Example 3: Retirement 1.3-15

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Example 3: Retirement a)If a typical retiree has retirement assets of \$500,000, how much can he or she withdraw annually if he or she wishes the assets to last 21 years? 1.3-16

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Example 3: Retirement 1.3-17

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Solution a) From the graph, we can see that for assets to last 21 years, about 6% of the assets can be withdrawn annually. The amount that can be withdrawn is Amount = 6% of assets Amount = 0.06(500,000) = \$30,000 Thus, about \$30,000 can be withdrawn annually. Example 3: Retirement 1.3-18

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Example 3: Retirement b)How much should a retiree have in assets if he or she wishes to withdraw \$25,000 annually and wishes his or her assets to last 18 years? 1.3-19

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Example 3: Retirement 1.3-20

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Solution b) From the graph, we can see that for assets to last 18 years, about 7% of the assets can be withdrawn annually. That amount has to equal \$25,000: 7% of assets = \$25,000 0.07  assets = \$25,000 assets = 25,000 ÷ 0.07 = 357,142.86 The retiree needs \$357,142.86 Example 3: Retirement 1.3-21

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Example 4: Determining a Tip The cost of Freddie Rojo’s meal before tax is \$28.00. a) If a 6 ½ % sales tax is added to his bill, determine the total cost of the meal including tax. 1.3-22

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Solution Change 6 ½ to a decimal: 0.065 Sales tax = 6 ½ % of meal Sales tax = 0.065(28.00) = 1.82 The total bill = cost of meal + sales tax Total bill = 28.00 + 1.82 = \$29.82 The bill including sales tax is \$29.82 Example 4: Determining a Tip 1.3-23

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Example 4: Determining a Tip The cost of Freddie Rojo’s meal before tax is \$28.00. b) If Freddie wants to leave a 10% tip on the pretax cost of the meal, how much should he leave? 1.3-24

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Solution To find 10% of any number, we multiply the number by 0.10 10% of pretax cost = 0.10(28.00) = 2.80 A simple way to find 10% of any number is to move the decimal point in the number one place to the left: 28.00  2.80 Example 4: Determining a Tip 1.3-25

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Example 4: Determining a Tip The cost of Freddie Rojo’s meal before tax is \$28.00. c) If he wants to leave a 15% tip on the pretax cost of the meal, how much should he leave? 1.3-26

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Solution To find 15% of \$28.00, multiply: 15% of \$28.00 – 0.15(28.00) = 4.20 Or to find 15%, find 10% and add it to ½ that amount: \$2.80 + = \$2.80 + \$1.40 = \$4.20 Example 4: Determining a Tip 1.3-27

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Example 6: Spraying Weed Killer The instructions on the Ortho Weed- B-Gon lawn weed killer indicate that to cover 1000 square feet (ft 2 ) of lawn, 20 teaspoons (tsp) of the weed killer should be mixed in 5 gallons (gal) of water. Ron Haines wishes to spray his lawn with the weed killer using his pressurized sprayer. a)How much weed killer should be mixed with 8 gal of water to get a solution of the proper strength? 1.3-28

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Solution Use: 20 teaspoons of weed killer is to be mixed with 5 gal water Example 6: Spraying Weed Killer Note: teaspoons and gallons are placed in the same relative positions. Replace the ? with an x. 1.3-29

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Solution Example 6: Spraying Weed Killer Ron must mix 32 tsp of weed killer with 8 gal of water. (32 tsp = 10 2/3 tablespoons = 2/3 cup) 1.3-30

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Example 6: Spraying Weed Killer The instructions on the Ortho Weed- B-Gon lawn weed killer indicate that to cover 1000 square feet (ft 2 ) of lawn, 20 teaspoons (tsp) of the weed killer should be mixed in 5 gallons (gal) of water. Ron Haines wishes to spray his lawn with the weed killer using his pressurized sprayer. b)How much weed killer is needed to cover an area of 2820 ft 2 of lawn? 1.3-31

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Solution Use: 1000 ft 2 requires 20 teaspoons of weed killer Example 6: Spraying Weed Killer Areas may be on top or bottom as long as they are in the same relative position. Replace the ? with an x. 1.3-32

Copyright 2013, 2010, 2007, Pearson, Education, Inc. Solution Example 6: Spraying Weed Killer Thus, 56.4 tsp are needed. 1.3-33