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trust123: Senior | Next Rank: 100 Posts; Posts: 34; Joined: Tue Apr 07, 2009 1:55 am

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by trust123 » Sun Aug 09, 2009 8:39 am

plz explain the concepts of std deviation ,, mean,, mode i m weak in this area........ i cn consistently score 47-49 in math section.......... i think the difference b/w me and 51 is this topic......so if any 1 can explain me thi topic i ll be really greatful

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Source: Beat The GMAT — Data Sufficiency | Sun Aug 09, 2009 8:39 am

real2008: Legendary Member; Posts: 527; Joined: Thu May 01, 2008 12:06 am; Thanked: 7 times

by real2008 » Sun Aug 09, 2009 9:27 am

is the answre D

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tom4lax: Master | Next Rank: 500 Posts; Posts: 175; Joined: Mon Feb 09, 2009 3:57 pm; Thanked: 4 times

by tom4lax » Tue Aug 11, 2009 4:59 am

I also got D. Key in on the underlined word, different.
Say we have the 5 numbers, A B C D E. Question is asking, is (D+E)/2>70? D+E>140?

Statement I
median is 70. If C=70, then D and E have to be at least 71 and 72. 71+72>140. Sufficient

Statement II
This one is easier to think about intuitively. If the average of the whole set is 70, and each number is different, then the two greatest numbers need to be at least 70 each in order to balance out A + B. Sufficient.