Question

一道GMAT的数学题

If Henry were to add 5 gallons of water to a tankthat is already 3/4 full of water, the tank would be 7/8 full. How many gallons of water would the tank holdif it were full?

A. 25
B. 40
C. 64
D. 80
E. 96

Answer 1

5÷（7/8-3/4）
=5÷1/8
=40
选B

追问

能不能解释下为什么。。。

追答

5 gallons
对应的分数为
7/8-3/4
求总量用除法
即
5÷（7/8-3/4）

Answer 2

let x be the volume of the tank
(7/8-3/4)x =5
x=40
ans: B

Answer 3

5/(7/8-3/4)=40