[問題]GWD6-Q10

[gimmy03]

DS:

When 200 gallons of oil were removed from a tank, the volume of oil left in the tank was 3/7 of the tank’s capacity. What was the tank’s capacity?

(1)Before the 200 gallons were removed, the volume of oil in the tank was 1/2 of the tank’s capacity.

(2)After the 200 gallons were removed, the volume of oil left in the tank was 1,600 gallons less than the tank’s capacity.

Ans: D

Why (2) is sufficent? Please help! 3Q~

[汪汪北鼻]

DS:

When 200 gallons of oil were removed from a tank, the volume of oil left in the tank was 3/7 of the tank’s capacity. What was the tank’s capacity?

(1)Before the 200 gallons were removed, the volume of oil in the tank was 1/2 of the tank’s capacity.

(2)After the 200 gallons were removed, the volume of oil left in the tank was 1,600 gallons less than the tank’s capacity.

Ans: D

Why (2) is sufficent? Please help! 3Q~

設X gallons在tank中
capacity is y
由題目x-200=3/7y
1)x=1/2y, 和原式聯立可解出y=2800
2)x-200=y-1600 , 和原式聯立可解出y=2800
thus, the answer is D

[gimmy03]

3Q 詳細的解說

[chris8888]

事實上不需要解聯立方程式

1. 200被移出前, 他是1/2, 所以200 / (1/2 - 3/7) = 2800

2. 200移出後, 距離滿水位1600, 表示4/7的capacity是空的, 1600 / (4/7) = 2800

OK~