Bunuel wrote:
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
Practice Questions
Question: 6
Page: 152
Difficulty: 600
Since an approximation is needed, and we cannot use a calculator, I would take that 138 billion represents only 80 percent of the full capacity. I know that my answer will be a slight overshoot. So, if 138 is 80%, then 10% is 138/8 = 34.5/2 = 17.25, and 100% will be 172.5 billion. My overshot answer is 172.5-124=48.5.
So, the correct answer should be 44.
Just to be on the safe side: (124+30)*0.8=154*0.8=123.2 and (124+44)*0.8=168*0.8= 134.4, so definitely, 44 is the correct answer.
By a second thought, if we think of "ball parking", then all we need are the last two tests above. It is clear that the answer should be greater than 14 (124+14=138, which is just 82% of full capacity). No need to calculate the full capacity and then the required difference, it is sufficient to check that (124 + the answer) * 0.8 is the closest to 138.
Not a pretty question...
Answer E
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