Two different groups of test-takers received scores on the

The problem says the values are normally distributed. Therefore 68% of all values fall within 1 standard deviation, 95% of all values fall within 2 standard deviations, and 99% of all values fall within 3 standard deviations.

Group A has a mean of 460 and a standard deviation of 20. So 1 standard deviation would be 440, so you are looking for values less than 440. Since you are dealing with only the left side of the curve you use 1/2 of 32 or 16%.

Group B has a mean of 520 and a standard deviation of 40. So it would take 2 standard deviations to get to 440 (520-80). Since you are dealing with the left side of the curve you use 1/2 of 5 or 2.5%.

Since you will be taking both 2.5% and 16% of a number use a number both go into like 400. 2.5% of 400=10 and 16% of 400=64. Since you can't have a fraction of a student and you want below scores of 440(not equal to them), use 9 and 63. Now you have 9/(63+9)=9/72=1/8. So the answer is B.

I had to look up the % tables and do a some calculations to get a number that worked well like 400. At first I got 5/37, but then I figured they wanted scores less than 440 so I decreased my values and ended up with an answer that was there. I really hope there isn't a question like this when I take the gmat.