Mean, median..

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Sprite_TM: Senior | Next Rank: 100 Posts; Posts: 79; Joined: Wed Jan 07, 2009 8:45 am; Thanked: 1 times

by Sprite_TM » Wed Jun 10, 2009 5:15 pm

ok. the question is something like this.

in a 12 month period, max rainfall was 12.2mm and minimum rainfall was 2.2. The mean is 3.5. What is the median?

a)3.2
b) 3.6
c)4.0
d) 4.6
e) 4.8 i think these were the numbers

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Source: Beat The GMAT — Problem Solving | Wed Jun 10, 2009 5:15 pm

fengjig: Junior | Next Rank: 30 Posts; Posts: 16; Joined: Wed Jun 10, 2009 12:26 am; Location: Hong Kong

by fengjig » Wed Jun 10, 2009 8:34 pm

I think the options you presented are all too big to be the median. 3.1 is a possible median.

Assume already known all the rainfalls for each month, put the 12 numbers in ascending order, Several key characters appear for the 2nd to the 11th number
1. sum of the 6th and 7th number = 2*median
2. 2.2<= 2nd-5th number<=6th number
7th number<= 8th-10th number<=12.2

Then just simply test each one of the answers and see if they can make both above condition true

Details pls see attached calc

Attachments

calc.xls: (14 KiB) Downloaded 129 times

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Sprite_TM: Senior | Next Rank: 100 Posts; Posts: 79; Joined: Wed Jan 07, 2009 8:45 am; Thanked: 1 times

by Sprite_TM » Thu Jun 11, 2009 7:21 am

this was a real test question on the test and i was pretty sure the numbers for a,b,d,e are correct. i was stumped and guessed 3.2

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gmatplayer: Master | Next Rank: 500 Posts; Posts: 103; Joined: Fri May 22, 2009 3:56 am; Thanked: 4 times; GMAT Score:470

by gmatplayer » Sat Jun 13, 2009 4:25 am

The way I think is if you take mean of highest & lowest number it is 7.2.
And since the mean is 3.5, definately the data is skewed toward lowest value which brings the mean down. This is possible only when the median of data must be less than 3.5
Answer = 3.2

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electrico: Senior | Next Rank: 100 Posts; Posts: 53; Joined: Tue Feb 17, 2009 11:14 pm; Location: India; Thanked: 2 times

by electrico » Thu Jun 18, 2009 6:50 pm

I go with gmatplaye's explanation..... it has to be less that 3.5...and only option is A.

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