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Josh has to run an electrical wire from point a to point b

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Josh has to run an electrical wire from point a to point b [#permalink] New post 28 Aug 2010, 09:58
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Question Stats:

71% (01:10) correct 28% (01:52) wrong based on 2 sessions
Josh has to run an electrical wire from point a to point b along a circuit that is restricted to the grid shown to the left. How many possible paths could Josh use that have the minimum possible length?

A. 8
B. 10
C. 12
D. 15
E. 16
[Reveal] Spoiler: OA

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Last edited by Bunuel on 08 Aug 2012, 00:57, edited 1 time in total.
Edited the question.
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Re: Grockit: similar to OG Quant qustion [#permalink] New post 28 Aug 2010, 10:05
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zisis wrote:
Josh has to run an electrical wire from point a to point b along a circuit that is restricted to the grid shown to the left. How many possible paths could Josh use that have the minimum possible length?

A 8
B 10
C 12
D 15
E 16




obv the answer can be found by counting the routes, but is there a better way?


You can notice that in order the length to be minimum wire should only go UP and RIGHT: namely twice UP and 4 times RIGHT.

So combination of UURRRR: # of permutations of 6 letters out of which there are 2 identical U's and 4 identical R's is \frac{6!}{2!4!}=15.

Answer: D.

Hope it's clear.
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Re: Grockit: similar to OG Quant qustion [#permalink] New post 28 Aug 2010, 10:34
Excellent approach.

Bunnel I was just wondering how much you got on Gmat? Have you given?
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Re: Grockit: similar to OG Quant qustion [#permalink] New post 29 Aug 2010, 05:48
Bunuel wrote:
zisis wrote:
Josh has to run an electrical wire from point a to point b along a circuit that is restricted to the grid shown to the left. How many possible paths could Josh use that have the minimum possible length?

A 8
B 10
C 12
D 15
E 16




obv the answer can be found by counting the routes, but is there a better way?


You can notice that in order the length to be minimum wire should only go UP and RIGHT: namely twice UP and 4 times RIGHT.

So combination of UURRRR: # of permutations of 6 letters out of which there are 2 identical U's and 4 identical R's is \frac{6!}{2!4!}=15.

Answer: D.

Hope it's clear.


thanks! thats exactly what i was looking for ! If i recall correcty, you must be the GMATclub combinations expert

[ :idea: :idea: IDEA :idea: :idea: how about we have experts stamps for certain individuals ! ;-) SC, combinations, RC, algebra etc....something the forum admins should consider...]
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Re: Grockit: similar to OG Quant qustion [#permalink] New post 29 Aug 2010, 09:04
He is expert in almost every topic of quant.
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Re: Grockit: similar to OG Quant qustion [#permalink] New post 29 Aug 2010, 10:18
lol...then he will have lots of "stamps" :p
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find the no of ways [#permalink] New post 23 Oct 2010, 06:48
hi all
please explain ..
if there is a rectangle and this rectangle is divided in to four equal rectangles by building roads inside it then how many ways are there with which one can reach from one corner to other diagonally opposite corner.
please try to explain in terms of combinations .like in terms of nCr etc.

thanks
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Re: find the no of ways [#permalink] New post 23 Oct 2010, 10:11
harshsingla wrote:
hi all
please explain ..
if there is a rectangle and this rectangle is divided in to four equal rectangles by building roads inside it then how many ways are there with which one can reach from one corner to other diagonally opposite corner.
please try to explain in terms of combinations .like in terms of nCr etc.

thanks


You need to find permutations of UURR = 4!/2!2! = 6
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Re: find the no of ways [#permalink] New post 23 Oct 2010, 10:21
but how 4c2..???
please explain!!
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Re: find the no of ways [#permalink] New post 23 Oct 2010, 10:27
harshsingla wrote:
but how 4c2..???
please explain!!



think of it like this
You have four moves to make to reach the opposite corner

two moves are up
and two moves are right

now, any order of moves would always get to the corner

the question really is that out of move1,2,3&4 which two you pick to be the Up move (the other two will be the right move). The ways to do this is C(4,2), choosing 2 out of 4.
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Re: find the no of ways   [#permalink] 23 Oct 2010, 10:27
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