At a book sale, all paperback books cost d dollars each and all hard books cost 2d dollars each. If Kate paid 7d dollars for 5 books at this sale, how many paperback books did she buy?

3 paperback books

Step-by-step explanation:

Let the number of paperback Kate bought be a and the number of hard books be b.

Given that she bought 5 books then

a + b = 5

Also, If Kate paid 7d dollars then

a * d + b * 2d = 7d

Divide through by d

a + 2b = 7

Hence we have 2 equations

a + b = 5

a + 2b = 7

subtract the first from the second

2b - b = 7 - 5

b = 2

since

a + b = 5

a + 2 = 5

a = 5 - 2

= 3

Recall that the number of paperback she bought is a hence this is 3

the answer is b

answer: the first graph

step-by-step explanation: