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Pls explain

by raju232007 » Sat Sep 06, 2008 11:15 am
A certain established organization has exactly 4096 members. A certain new organization has exactly 4 members. Every 5 months the membership of the established organization increases by 100 percent. Every 10 months the membership of the new organization increases by 700 percent. New members join the organizations only on the last day of each 5- or 10-month period. Assuming that no member leaves the organizations, after how many months will the two groups have exactly the same number of members?

(A) 20
(B) 40
(C) 50
(D) 80
(E) 100

OA is E
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Re: Pls explain

by parallel_chase » Mon Sep 08, 2008 9:59 am
raju232007 wrote:A certain established organization has exactly 4096 members. A certain new organization has exactly 4 members. Every 5 months the membership of the established organization increases by 100 percent. Every 10 months the membership of the new organization increases by 700 percent. New members join the organizations only on the last day of each 5- or 10-month period. Assuming that no member leaves the organizations, after how many months will the two groups have exactly the same number of members?

(A) 20
(B) 40
(C) 50
(D) 80
(E) 100

OA is E
EO - established organization
NO - new organization

EO - 100% in 5 months - 2 times in 5 months - 4 times in 10 months
NO - 700% in 10 months - 8 times in 10 months

4096*4^n = 4*8^n

4096/4 = 8^n / 4^n

1024 = 2^n

n=10

10*10 = 100 months

Hence E is the answer.
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