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Averages

by MI3 » Sat Jul 16, 2011 4:58 am
Q. 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

IMO - B, am I correct?
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by MBA.Aspirant » Sat Jul 16, 2011 5:14 am
MI3 wrote:Q. 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

IMO - B, am I correct?
I'm getting C) 200

mean increased by 50% to 75, so it was 50

mean was 50 when 5 ppl contributed, so sum was 250

sum when John contributed is 75*6 = 450

so his contribution is 450 -250 = 200
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by MI3 » Sat Jul 16, 2011 5:16 am
MBA.Aspirant wrote:
MI3 wrote:Q. 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

IMO - B, am I correct?
I'm getting C) 200

mean increased by 50% to 75, so it was 50

mean was 50 when 5 ppl contributed, so sum was 250

sum when John contributed is 75*6 = 450

so his contribution is 450 -250 = 200
Yes, I think you are right - I may have made a silly mistake of multiplying (50 * 6) instead of (50 * 5), which is where the difference of 50 is appearing. Many thanks.
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