500 ps test27#13

[dunkin77]

13. A rainstorm increased the amount of water stored in State J reservoirs from 124 billion gallons to 138 billion gallons. If the storm increased the amount of water in the reservoirs to 82 percent of total capacity, approximately how many billion gallons of water were the reservoirs short of total capacity prior to the storm?
(A) 9 (B) 14 (C) 25
(D) 30 (E) 44

Hi,
for some reason my answer was C) but actually the correct answer is E) -- can anyone explain?

[rajeshvellanki]

138-124= 14 gallons increase

Given that storm increased the reservoirs to 82% ==> 138=82% of total capapcity X

it means it is 18% short from it being a full tank

82%(which is 138)+18%=100% ==>fulltank

138 --> 82%
? --> 18%
( 138*18)/82=30.3

==> Gallons short of total capcity before storm= 14 + 30.3 =14+30(approx) =44gallons

PS: If you draw a tank pic and lay out the problem it is very easy to solve.

[Shaki]

Why not to go through an easier way:

138 ------> 82%
x -------> 100%

from here, x~168

168-124=44 (E)

[Shaki]

Why not to go through an easier way:

138 ------> 82%
x -------> 100%

from here, x~168

168-124=44 (E)

[Cybermusings]

138 gallons - 82% capacity
Thus total capacity = 13800/82 = 6900/41
Capacity diff = 6900/41 - 124 = 168.2 - 124 = 168 - 124 = 44 (Approximately)