help me please.!!!

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shikh: Senior | Next Rank: 100 Posts; Posts: 48; Joined: Sun Jul 17, 2011 12:04 am

help me please.!!!

by shikh » Sat Nov 12, 2011 12:30 am

A group of 10 people plan to contribute equally to pay fora friend's gift that costs G dollars. If nadditional people want to contribute to pay for the gift, the required contribution per person will be reduced by how many dollars?
(A)Gn/100+10n
(B)10+n/Gn
(C)10G+Gn/n
(D)Gn+10G/GN-10
(E)10G/n^2+10n :roll:
answer after discussion...[/img]

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Source: Beat The GMAT — Problem Solving | Sat Nov 12, 2011 12:30 am

shankar.ashwin: Legendary Member; Posts: 966; Joined: Sat Jan 02, 2010 8:06 am; Thanked: 230 times; Followed by:21 members

by shankar.ashwin » Sat Nov 12, 2011 12:41 am

Just substitute easy numbers.

Let the gift cost $100, so initially everyone pays $10 each.

Let n = 10 (10 additional people contribute), the cost per head now will be 100/20 = $5.

Sub G = 100 and n = 10 in the answer choices, you should get 5 as answer. Only A satisfies IMO.

Infact you could even use smaller numbers.

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smackmartine: Legendary Member; Posts: 516; Joined: Fri Jul 31, 2009 3:22 pm; Thanked: 112 times; Followed by:13 members

by smackmartine » Sat Nov 12, 2011 12:47 am

IMO A
Cost of the gift = G
Total people initially = 10
Cost per head = G/10

Extra people who want to contribute = n
So, total # of people = 10+n
Cost per head now= G/(10+n)

Notice that G/10 > G/(10+n) [now each person has to contribute less]

So, contribution per person will be reduced = [G/10]- [G/(10+n)] = Gn/10(10+n)=Gn/100+10n

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