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Current Student
Joined: 11 Apr 2013
Posts: 52

Kudos [?]: 28 [0], given: 13

Schools: Booth '17 (M)

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12 Jun 2013, 22:18
This problem single handedly screwed my quant section this week. I can't remember the exact numbers involved, but it was something like:

'n' parents split the \$300 cost of a school trip equally. If the school had three less parents, each the parents would each pay an additional \$3. Find 'n'

my method was...
300/n = x
300 = nx

and

300/n-3 = x +3
300 = nx + 3n - 3x - 9
sub nx = 300
300 = 300 + 3n - 3x - 9
9 = 3(n - x)
3 = n - x
.... then I don't know, not sure if I'm even doing this right. I think it was just jitters, but i spent 5 full minutes on this and finally just guessed.

My question is: what's the correct method here and has anyone seen a question similar to this so I can work it out with numbers that actually add up? This seems really easy but I'm just not getting something and it's driving me insane. Thanks!

Kudos [?]: 28 [0], given: 13

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21 Dec 2013, 02:44
1
KUDOS
Hi,

Approach is right.. some data is wrong as solving it is leading to irrational roots. To correct data, let n decreases by 5 and x increases by 5,
then we get 5 = n-x by your approach (instead of 3= n-x)

Next step is to put x= n-5 in the equation nx=300 , solve quadratic equation to get n = 20 and x =15

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Feel free to write if you have any further queries.

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Neha Singh
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Kudos [?]: 113 [1], given: 6

Current Student
Joined: 11 Apr 2013
Posts: 52

Kudos [?]: 28 [0], given: 13

Schools: Booth '17 (M)

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21 Dec 2013, 19:29
nehasingh1020 wrote:
Hi,

Approach is right.. some data is wrong as solving it is leading to irrational roots. To correct data, let n decreases by 5 and x increases by 5,
then we get 5 = n-x by your approach (instead of 3= n-x)

Next step is to put x= n-5 in the equation nx=300 , solve quadratic equation to get n = 20 and x =15

To know more about online GMAT classes visit http://bit.ly/XKxOPd

Feel free to write if you have any further queries.

Cheers!
Neha Singh

Thanks Neha!!! I think on the actual test the problem was that I wasn't resubbing after the first substitution in order to get a quadratic and solve that way. I'm used to two variable/two equation problems being a little more straightforward. Thanks for clarifying.

Kudos [?]: 28 [0], given: 13

Re: Help!   [#permalink] 21 Dec 2013, 19:29
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