Exercise 7 Page 49

Practice makes perfect

a We subscribe to cable TV while our friend chose satellite TV. We want to see if their expenses for a year are less than ours. First, we will define a variable. Let x be the number of months for which cable TV is purchased. x Since we pay 45 dollars per month, we can write the expression representing the entire cost.

45x The price our friend paid consists of two parts.

A flat fee of 99 dollars for a satellite dish
A flat rate of 36 dollars per month.

Now we can write the following expression representing how much our friend paid. 36x+ 99 We will now set the expressions equal to each other. Solving the equation will tell us when we have paid the same amount as our friend.

45x=36x+99

SubEqn

LHS-36x=RHS-36x

9x=99

DivEqn

.LHS /9.=.RHS /9.

x=11

The solution x=11 means that we will have paid the same total amount as our friend at 11 months of service.

b To determine which service costs more for one year (or twelve months) we can substitute x=12 into the expressions from Part A and evaluate.

Service	Expression	x=12	Cost for one year ($)
Cable	45x	45 ( 12)	540
Satellite	36x+99	36( 12)+99	531

Looking at the information in the table, we can see that satellite costs less than cable. This means that our friend is correct.

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Exercises p.48-49

Exercise 7 Page 49

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