Writing Algebraic Expressions to Solve Word Problems.

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

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• 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.

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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

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Now its 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!
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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!
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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?

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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!

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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.

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Homework

• You KNEW it was coming!
• ?

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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)

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This Slide Show can be found on my wiki at

• http//meehanwiki.wikispaces.com/7thGrade-Mrs.O
  lds-Math