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average is 3x + 4

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average is 3x + 4

by hansoo » Mon Sep 21, 2009 3:27 pm
The average (arithmetic mean) of five numbers is 3x + 4. If one of the numbers is 7x - 4, what is the average of the other four numbers?

a) 1.6x + 3.2
b) 1.6x + 4.8
c) 2x + 4
d) 2x + 4
e) 4x + 8
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by sunnyjohn » Mon Sep 21, 2009 6:32 pm
5(3x + 4 ) - 7x + 4
---------------------
4

==>
8x + 24
-------
4


==>

2x + 6
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Missing answer

by nand358 » Mon Sep 21, 2009 6:36 pm
The answer is (2x + 6)

(4*AM of 4 numbers) + 7x -4 = 5*(3x + 4)

So, Arithmetic mean of 4 numbers = (8x + 24)/4 = 2x + 6

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by hansoo » Sat Sep 26, 2009 4:24 pm
Great work guys! The official answer is D.

Here's a text explanation:

Image

And here's a video explanation: GMAT video
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