Kaplan 800 Word problems

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punitkaur: Master | Next Rank: 500 Posts; Posts: 168; Joined: Mon Apr 13, 2009 6:48 pm; Thanked: 6 times

by punitkaur » Tue Nov 10, 2009 3:23 pm

A batch of cookies was divided among 3 tins:2/3 of all the cookies were placed in either the blue tin or the green tin and the rest were placed in the red tin. If 1/4 of all cookies were placed in blue tin,

what fraction of the cookies that were placed in the other tins were placed in the green tin.

very simple question about fractions.

My formula for the answer was = g/b+r

where g- no of green cookies
b-no of blue cookies
r-no of red cookies.

The answer says the final calcuation should be g/g+r

why is the denominator g+r. Doesn't other cookies mean b+r?

OA is 5/9. and my answer was 5/7

Someone please explain. I think I am not getting the last sentence of the question correct.

Source: Beat The GMAT — Problem Solving | Tue Nov 10, 2009 3:23 pm

satish.nagdev: Master | Next Rank: 500 Posts; Posts: 130; Joined: Sat Dec 29, 2007 5:35 am; Location: SGP; Thanked: 5 times

by satish.nagdev » Tue Nov 10, 2009 7:40 pm

I approached it by putting values
lets say 24 = total number,
2/3 = 16 (blue + green)
1/3 = 8 , red
blue = 1/4 of 24 = 6, so green = 10

green/rest = green / (red + blue)
= 10/ (6+8) = 5/7

Wounded by GMAT but not dead

punitkaur: Master | Next Rank: 500 Posts; Posts: 168; Joined: Mon Apr 13, 2009 6:48 pm; Thanked: 6 times

by punitkaur » Wed Nov 11, 2009 3:49 am

ya its a straighforward question on fractions, but the formula used in the book is

green/ green + red. I dont understand why.

OA is 5/9

jd006h: Newbie | Next Rank: 10 Posts; Posts: 3; Joined: Wed Nov 11, 2009 5:36 am

explanation

by jd006h » Wed Nov 11, 2009 5:49 am

if 2/3 of the original cookies are placed in blue or green, and 1/4 go in blue, then 2/3 - 1/4 = 8/12 - 3/12 = 5/12 in green. assuming there were 12 cookies originally, 3 are in blue, 5 in green, so the other 4 must go in red. the question asks of the the cookies not placed in blue, what fraction were placed in green. so if there are 9 cookies not placed in blue, and 5 of them are placed in green, 5/9 of the remaining cookies are in green.

mp2437: Master | Next Rank: 500 Posts; Posts: 177; Joined: Thu Aug 14, 2008 11:59 am; Thanked: 25 times

by mp2437 » Wed Nov 11, 2009 11:43 am

"If 1/4 of all cookies were placed in blue tin, what fraction of the cookies that were placed in the other tins were placed in the green tin. "

It's a matter of reading the question - it first mentions that 1/4 was placed in blue, so the "other" ones are green and red. Then it says what fraction of those placed in other (red + green) are actually green.

So g/(g+r) is your answer.

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