DS with percentage change

Expert replies

HarvardDreamin: Senior | Next Rank: 100 Posts; Posts: 93; Joined: Sun Jan 27, 2008 1:35 am; Thanked: 2 times

by HarvardDreamin » Thu Mar 20, 2008 12:32 pm

q9) A parent established a college fund for his daughter. Each year the parent made a contribution to the fund, and each year he increased his contribution by a constant amount. If he made a contribution of $800 in the first year, by what amount did the parent increase his contribution to the fund each year?
(1) The parent’s contribution to the fund in the 18th year was $7600.
(2) The parent’s contribution to the fund in the 7th year was twice what it was in
the 3rd year.

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Source: Beat The GMAT — Data Sufficiency | Thu Mar 20, 2008 12:32 pm

madhavi: Senior | Next Rank: 100 Posts; Posts: 57; Joined: Tue Jun 26, 2007 11:33 pm; Thanked: 4 times

by madhavi » Fri Mar 21, 2008 6:08 am

From the given data in the question we know that, the amount contributed in any year n is 800 + (n-1)*a

where a is the constant amount increased each year

When we consider 1,

800 + 17(a)=7600
Thus, we can find a. Hence, answer boild down to A or D

When we consider 2,

800 +6(a)= 2*(800 +2(a))
Thus we can find a.

Hence, each statement alone is sufficient. Answer is D.

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HarvardDreamin: Senior | Next Rank: 100 Posts; Posts: 93; Joined: Sun Jan 27, 2008 1:35 am; Thanked: 2 times

by HarvardDreamin » Sat Mar 22, 2008 2:57 pm

madhavi wrote:From the given data in the question we know that, the amount contributed in any year n is 800 + (n-1)*a

where a is the constant amount increased each year

When we consider 1,

800 + 17(a)=7600
Thus, we can find a. Hence, answer boild down to A or D

When we consider 2,

800 +6(a)= 2*(800 +2(a))
Thus we can find a.

Hence, each statement alone is sufficient. Answer is D.

Thanks
https://goal-mba.blocked

Thanks!

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