List S and list T each contain 5 positive integers, and for each list the average of the integers in the list is 40. If the integers 30,40 and 50 are in both lists , is the standard deviation of the integers in list S greater than the standard deviation of the integers in list T ?
(1)The integer 25 is in list S
(2)The integer 45 is in list T
And C
What is the fastest approach ? What is the best way to calculate SD here?
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You never need to calculate SD on the GMAT. In DS, we're just seeing if we have enough info to calculate.moneyman wrote:List S and list T each contain 5 positive integers, and for each list the average of the integers in the list is 40. If the integers 30,40 and 50 are in both lists , is the standard deviation of the integers in list S greater than the standard deviation of the integers in list T ?
(1)The integer 25 is in list S
(2)The integer 45 is in list T
And C
What is the fastest approach ? What is the best way to calculate SD here?
In this question, if we know what the sets are, we can certainly calculate SD.
We already know 3/5 numbers on each list, so we're not far off. We also know the average of each list, and therefore the sum (= avg * # of terms).
(1) S contains 25. This allows us to determine the 5th member of S, but we don't know enough about T.
(2) T contains 45. This allows us to determine the 5th member of T, but we don't know enough about S.
Together: We know the full sets for S and T. If we know all the terms in a set, we can calculate ANYTHING about that set, including SD. If we can calculate both SDs, we can certainly answer the question: choose (c).
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