how many books did he buy

Question

Patrick has $84 to spend on gifts. He must buy 8 gifts. He plans to buy storybooks that

cost either $8 or $12. How many of each book can he buy?

Answer 1

8x + 12y = 84

4x + 6y = 42

2x + 3y = 21

3y = 21 - 2x

y = (21 -2x)/3

x y

--------------------

0 7 <--- unacceptable

1 6 <--- unacceptable

2 5 <--- unacceptable

3 5 <--- unacceptable

4 4

5 3

6 3

7 2

8 1

9 1

10 0