How many 300 MB flash drives did John buy?

Question

John bought some flash drives, some had a capacity of 400 MB and others 300 MB. If John bought 14 flash drives in total and the combined capacity of the flash drives are 4700 MB, how many 300 MB flash drives did John buy?

 

A. 6

B. 7

C. 8

D.9

Answer 1

Let x = the number of 400 MB flash drives John bought

Let y = the number of 300 MB flash drives John bought

x + y = 14     x = 14 - y

400x + 300y = 4700

400(14 - y) + 300y = 4700

5600 - 400y + 300y  = 4700

-100y = -900

y = 9 flash drives