Hi LUANDATO,

We're told that during the first two weeks of January, the TOTAL rainfall in Springdale was 15 inches and that the rainfall during the second week was 1.5 times the rainfall during the first week. We're asked for the rainfall (in inches) during the SECOND week of January. In these types of questions, it's likely that the total amount of rain for EACH week will be among the five answer choices, so you have to make sure to answer the question that is ASKED. In addition, when the 'numbers' involved are relatively small, you might find it fastest to simply 'brute force' the arithmetic until you answer the given question.

Since the rainfall in the second week is 1.5 times the rainfall in the first week, the possible TOTAL amounts of rain could be...
Wk 1. = 1 inch, Wk 2 = 1.5 inches, TOTAL = 2.5 inches
Wk 1 = 2 inches, Wk 2 = 3 inches, TOTAL = 5 inches
Etc.

Notice with the second example that the TOTAL is exactly 1/3 of what we need it to be. To save a few steps, we can now 'triple' each of those numbers....
Wk 1 = 6 inch, Wk 2 = 9 inches, TOTAL = 15 inches

And now we know how many inches it rained in the second week...

Final Answer: C

GMAT assassins aren't born, they're made,
Rich

LUANDATO wrote:During the first two weeks of January, the total rainfall in Springdale was 15 inches. If the rainfall during the second week was 1.5 times the rainfall during the first week, what was the rainfall during the second week of January?

A. 5 inches
B. 6 inches
C. 9 inches
D. 10 inches
E. 12 inches

We can let the rainfall in the first week = a and the rainfall in the second week = b and create the following two equations:

a + b = 15

and

b = 1.5a

Substituting, we have:

a + 1.5a = 15

2.5a = 15

a = 6

Thus, the rainfall in the second week was 15 - 6 = 9 inches.

Answer: C