Means of lists of odd and even integers

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jzebra10: Junior | Next Rank: 30 Posts; Posts: 12; Joined: Tue Nov 08, 2011 4:42 am

by jzebra10 » Sun Nov 20, 2011 1:41 am

Please help. I don't know how to solve.

List S consists of 10 consecutive odd integers, and like T consists of 5 consecutive even integers. If the least integer in S is 7 more than the least integer in T, how much greater is the average of the integers in S that the average of the integers in T?

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by gmatclubmember » Sun Nov 20, 2011 1:59 am

List S=m+7,m+9,...,m+25
T = m,m+2,m+4,...,m+8.
Avg(S)=m+16 and Avg(T)=m+4
Avg of S is 12 more than avg of T.

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by GMATGuruNY » Sun Nov 20, 2011 4:15 am

jzebra10 wrote:Please help. I don't know how to solve.

List S consists of 10 consecutive odd integers, and like T consists of 5 consecutive even integers. If the least integer in S is 7 more than the least integer in T, how much greater is the average of the integers in S that the average of the integers in T?

When numbers are evenly spaced, THE AVERAGE = THE MEDIAN.
Let T = 2,4,6,8,10.
Average = median = 6.

The least value in S = 2+7 = 9.
S = 9,11,13,15,17,19...
Average = median = (17+19)/2 = 18.

Average in S - average in T = 18-6 = 12.

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