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700-800 level problem Statistics

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700-800 level problem Statistics [#permalink]  22 Jan 2010, 11:16
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54% (02:03) correct 45% (00:41) wrong based on 2 sessions
If john makes a contribution to a charity fund at school, the average contribution size will increase by 50% reaching $75 per person.If there were 5 other contributions made before john's,what is the size of his donation? a)$100
b)$150 c)$200
d)$250 e)$450

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Re: 700-800 level problem Statistics [#permalink]  22 Jan 2010, 11:20
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Cavg = average contribution before John

Cavg*1.5 = 75, therefore the average cont is $50 before John. If he needs to increase the average contribution by$25, he must put in $25 for each of the 5 people. so$125.
But, he also has to put in the average for himself (the sixth person), so add $75. So$200 is your answer.
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Re: 700-800 level problem Statistics [#permalink]  22 Jan 2010, 11:33
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yes 200 is the ans.

final avg = 75 = 1.5 of old

i.e old avg = 50 = total of five/5

total of five = 250

new avg = 75 = total of six/6

total of 6 = 450

so John's contribution = 450-250 =200
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Re: 700-800 level problem Statistics [#permalink]  22 Jan 2010, 11:35
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GMAT10 wrote:
If john makes a contribution to a charity fund at school, the average contribution size will increase by 50% reaching $75 per person.If there were 5 other contributions made before john's,what is the size of his donation? a)$100
b)$150 c)$200
d)$250 e)$450

Let a be the average contribution size before John makes his contribution.
Let c be the total contribution size before John makes his contribution.
Let x be John's contribution.

1.5a=75 --> a=50

a=50=\frac{c}{5} --> c=250

\frac{c+x}{6}=75 --> \frac{250+x}{6}=75 --> x=200

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Re: 700-800 level problem Statistics   [#permalink] 22 Jan 2010, 11:35
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