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Fractions.....How to ATTACK this type?!

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by smclean23 » Sat Jul 12, 2008 9:02 am
If r=1+1/3+1/9+1/27+1/81 and s=1+1/3(r) , then s exceeds r by
(A) 1/3 (B) 1/6 (C) 1/9
(D) 1/27 (E) 1/81


I've tried solving this problem and it takes me more than I should. I know the GMAT doesn't make you do long calculations, so how should I go about attacking this situation?

THANKS!
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e) 1/81

by hakyology » Sat Jul 12, 2008 12:07 pm
r= 1+ 1/3 + 1/9 + 1/27 + 1/81 in other words,
r= 1/3^0 + 1/3^1 + 1/3^2 + 1/3^3 + 1/3^4

s= a + 1/3 times r

put r into S equation.

s= 1 + 1/3 (1/3^0 + 1/3^1 + 1/3^2 + 1/3^3 + 1/3^4)
s= 1 + 1/3^1+ 1/3^2 + 1/3^3 + 1/3^4 + 1/3^5
s= 1/3^0 + 1/3^1 + 1/3^2 + 1/3^3 + 1/3^4 + 1/3^5

compare r with s

r and s are the same except 1/3^5

there it exceeds by 1/3^5.

close one is 1/81.
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by sudhir3127 » Mon Jul 14, 2008 1:45 am
hey can any one solve this ... my approach was exactly the same as that of the previous poster...

i end up getting 1/243 which 1/3^5.. but there no option like that...

are the answer choices wrong? or me missing anything?

ru sure the question you have posted is right ? i find it discussed on this forum .. here goes the link..

https://www.beatthegmat.com/fractions-t13346.html
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by asigheartau » Mon Jul 14, 2008 5:53 am
sudhir3127 wrote:hey can any one solve this ... my approach was exactly the same as that of the previous poster...

i end up getting 1/243 which 1/3^5.. but there no option like that...

are the answer choices wrong? or me missing anything?

ru sure the question you have posted is right ? i find it discussed on this forum .. here goes the link..

https://www.beatthegmat.com/fractions-t13346.html
the post you were mentioning does make much more sense. the answer is 1/3^4 but the question is different. There is not 1/81 at the begining of the problem=>

r=1+1/3+1/9+1/27
S=1+1/3 times R

If the question is the way it is posted here, the answer would be 1/3^5 which is not offered.
Alin Sigheartau
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