Last Updated on May 3, 2023
GMAT OFFICIAL GUIDE PS
Solution:
We are given that the water increased from 124 billion gallons to 138 billion gallons. We also know that 138 billion gallons is 82% of the total capacity. Let’s translate this information into an equation, where T = total capacity. We translate the sentence “138 billion gallons is 82% of total capacity” as 138 = (0.82)T, remembering that “is” means “equals” and “of” means “multiply.”
However, we are told to APPROXIMATE. So, instead of using the equation 0.82T = 138, we can instead use 0.8T = 136. Note that I chose 136 because I know that it is divisible by 8, but you could just as easily use 138 and ignore the decimal values. Now we need to solve for T.
T = 136/0.8
T = 1360/8
T = 170
The total capacity is approximately 170 billion gallons. It follows that the reservoirs were approximately 170 – 124 = 46 billion gallons short of capacity prior to the storm.
From our approximated answer, we see that answer choice E (44) is closest.
Answer: E
