The rainfall in City M during May of last year was 3 times the average (arithmetic mean) monthly rainfall for the other

[BTGmoderatorDC]

The rainfall in City M during May of last year was 3 times the average (arithmetic mean) monthly rainfall for the other 11 months of last year. If the average monthly rainfall for last year was 3.5 inches, what was the rainfall, in inches, in City M during May?

A. 1.5
B. 2
C. 4.5
D. 6
E. 9


OA E

Source: GMAT Prep

[Brent@GMATPrepNow]

The rainfall in City M during May of last year was 3 times the average (arithmetic mean) monthly rainfall for the other 11 months of last year. If the average monthly rainfall for last year was 3.5 inches, what was the rainfall, in inches, in City M during May?

A. 1.5
B. 2
C. 4.5
D. 6
E. 9


OA E

Source: GMAT Prep

Let k = the rainfall (in inches) for EACH MONTH last year excluding May
This means 3k = the rainfall (in inches) in May last year
So, the TOTAL rainfall = 11k + 3k = 14k

If the average monthly rainfall for last year was 3.5 inches, we can write: 14k/12 = 3.5
Multiply both sides of the equation by 12 to get: 14k = 42
Divide both sides by 14 to get: k = 42/14 = 3

This means each month, excluding May, received 3 inches of rainfall.
So the rainfall in May = 3 x 3 = 9 inches.

Answer: E