Question

A man bought 42 stamps, some 13¢ and some 18¢. How many of each kind did he buy if the cost was $6.66? If x represents the number of 13 cent stamps and y the 18 cent stamps, which system represents the problem?

Answer 1

18 stamps of 13 cent

24 stamps of 18 cent

Explanation:

we have to solve the following system:

x + y = 42 equation (1)

13x + 18y = 666 equation (2)

(1) ⇒ y = 42 - x

We substitute y by 42 - x in equation (2) :

13x + 18(42 - x) = 666

⇔ 13x + 756 - 18x = 666

⇔ -5x + 756 = 666

⇔ -5x = 666 - 756

⇔ -5x = -90

⇔ x = 18

…………………………

Then

y = 42 - x

= 42 - 18

= 24