Writing Algebraic Expressions to Solve Word Problems. How many minutes in 1 hour, 14 hours, in "n" hours?

Algebra is used every day to solve everyday problems. For example: You have a job and you get paid $8.25 an hour. You want to figure out how much pay you will receive if you worked 16 hours.

You can write in words, I get paid $8.25 for every hour I work. Algebraically, you would write: $8.25h which means 8.25 TIMES the number of hours you worked.

You should always write the formula FIRST for every question SO, you would write $8.25h = pay Then, substitute the number of hours into the formula. $8.25(16) = p (pay) Calculate the result Your pay would be $132.00 Write your answer as p = $132.00

Now it’s your turn. Using the formula, calculate your pay if you worked: 20 hours? 32 hours? 18.5 hours? 22 hours? 110 hours? Every question must start with the formula $8.25h = p Then substitute into the formula the hours that you worked. Remember the answer is MONEY and should be in that form!

Now the same question with a twist! If you got paid $189.75, how many hours did you work? You get paid $8.25 an hour. You can divide the pay by your rate of pay, ($8.25) to get the number of hours you worked. Algebraically, it would look like this. Calculate and you find: You worked, 23 hours!

New Problems Some problems require that you know basic facts. How many seconds in a minute? How many minutes in an hour? How many hours in a day? How many days in a week? How many days in a year? How many weeks in a year? How many months in a year? How many centimetres in a metre? How many metres in a kilometre?

How Many Days in Three Weeks? Since you know that there are 7 days in a week, you can write: 7 days X the number of weeks = the number of days in a week. Or Algebraically: 7(w) = d Substitute into the formula what you know. 7(3)= d Calculate d = 21 There are 21 days in three weeks!

How many hours in four days? There are 24 hours in one day. So 24d = hours in day 24 (4) = h h = 96 There are 96 hours in 4 days.

Homework You KNEW it was coming! 

Using the facts, write a formula for each and solve. How many days in 3 weeks? How many hours in 4 days? How many cm in 1500 metres? How many months in 13 years? How many weeks in 7 years? How many years in 3250 weeks? (careful) How many years in 250 months? (careful) How many minutes in 4 hours? How many hours in 17 days? How many kilometres in 4509 metres? (careful)

This Slide Show can be found at February Homework on our Math Web Site at: https://hamptongrade8math.wikispaces.com/