Grade 9 : Math : Word problem on Linear inequivalities

 A man bought x boxes of doughnuts for $3.49 each, he paid with a $50 bill and received the correct amount of change. If he received more than $10 but less than $20, which inequalities represent the number of boxes of doughnuts he could have bought?

A. 9 ≤ x ≤ 11
B. 8 ≤ x ≤ 12
C. 8 ≤ x ≤ 11
D. 9 ≤ x ≤ 12

Solution

By the given information,

Received amount = total amount paid - x*3.49

                         = 50 - 3.49x

10 ≤ 50 - 3.49x ≤ 20

Hence option A) 9 ≤ x ≤ 11 is the answer.