Hero8888 wrote:
See the question in attached pic.
Official explanation (SAT):
In Class A, the majority of scores are 3 and 4, with only a few scores of 0, 1, 2, and 5; the average score is between 3 and 4. In Class B, the scores are evenly spread out, with many scores not close to the average score, which is 2.5. Because the scores in Class A are more closely clustered around the mean, the standard deviation of the scores in Class A is smaller. The correct answer is choice A.
This is SAT question. Many people say that SAT math is easier than that of GMAT. According to what I learned on GMAT the right answer is B, because the smallest standard deviation = 0. According to SAT the right answer is A, althought the set A has positive standard deviation which is greater than 0 (s.d. of set B).
Is there any mistake in my thoughts?
Yes, there is a mistake in your analysis of the figure..
In B the SD is not 0, you are not finding SD of 4,4,4,4,4 but of 0,0,0,0,1,1,1,1,2,2,2......5,5,5,5
So they are evenly spread around 2.5
On other hand SD of A is based on 0,1,2,2,2,,3,3,3,3,....,5..
Here max of the numbers are closer to 2.5 with 8 of them at 3 and at 4.. so SD will be lesser for A
Hope it helps
_________________
1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html
4) Base while finding % increase and % decrease : https://gmatclub.com/forum/percentage-increase-decrease-what-should-be-the-denominator-287528.html
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