solve this inequality

Question

Lisa is checking out at the bookstore. Each book (b) costs $1.50 and she has a $5 off coupon she can use. She wants to spend $25 or less in the bookstore. How many books can Lisa buy?

 

Answer 1

Alternatively Lisa gets $5.00 off of the price of the books. So

$1.5b - $5.00<=$25.00

$1.5b<= $30.00

b=20

Answer 2

Lisa is checking out at the bookstore. Each book (b) costs $1.50 and she has a $5 off coupon she can use. She wants to spend $25 or less in the bookstore. How many books can Lisa buy?

Let's construct the inequality is small steps:

"spend $25 or less" means spend ≤ $25 [note that she can spend exactly $25]

spend = the amount Lisa spends.

"each book (b) costs $1.50"

b = number of books Lisa can buy

$1.50*b is the amount that Lisa can spend

So, far ... $1.50b ≤ $25.00

ALSO, "she has a $5 off coupon"

Now, $1.50b ≤ ( $25.00 - $5.00 )

$1.50b ≤ $20.00 [subtract +5 retains the sense of the inequality]

b ≤ 13 Lisa may buy 13 or fewer books.

Since $20.00 / $1.50 is 13.333..., Liza may buy 13 or fewer books (b must be an integer).