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Wrong OA? Please confirm

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Wrong OA? Please confirm

by bacali » Sat Nov 29, 2008 6:41 am
What was the percent increase in the average (arithmetic mean) contribution per member of a certain public radio station from 1985 to 1995 ?

(1) Total contributions by members increased from $505,210 in 1985 to $1,225,890 in 1995.
(2) The number of members exactly doubled from 1985 to 1995.


OA: [spoiler] C

I have it as E. Can someone please explain? Is the OA wrong??

Thanks[/spoiler]
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Source: — Data Sufficiency |
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by bluementor » Sat Nov 29, 2008 8:30 am
Hi Bacali, the OA is correct.

Lets define the following:

Total members in 1985 = a
Total members in 1995 = b
Total contributions in 1985 = x
Total contributions in 1995 = y

The % increase in the avg contribution per member from 1985 to 1995 can be calculated as follows:

100*((y/b) - (x/a))/(x/a)

I suppose you are clear about the individual statements being insufficient on their own.

Combining both statements together, you have:
1. the values of x and y
2. b=2a

When you insert this info into the equation above, you will see that b will be cancelled out and you will arive at a definite value.

C

-BM-
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by Neo2000 » Sat Nov 29, 2008 8:46 am
Percentage Increase =( (Final - Initial)/Initial ) * 100

We know the initial and final contribution
Let initial population = X then final population = 2x
You can get an expression for Average now

[spoiler]If you substitute in the above equation, X will cancel out leaving you with an expression that is solve-able

Hence "C"[/spoiler]
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