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Dek
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Lindsay can paint 1/x of a certain room in 20 minutes. What 01 Jun 2007, 09:45
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Lindsay can paint 1/x of a certain room in 20 minutes. What fraction of the same room can Joseph paint in 20 minutes if the two of them can paint the room in an hour, working together at their respective rates?

a. 1/3x
b. 3x/x – 3
c. x – 3/3x
d. x/x – 3
e. x – 3



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KillerSquirrel
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Lindsay can paint 1/x of a certain room in 20 minutes. What 01 Jun 2007, 10:15
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Lindsay can paint 1/x of a certain room in 20 minutes. so Lindsay can paint in one hour 3/x of the room. In one hour Lindsay & Joseph can paint:

3/x+(1-3/x) = L + J

we need to know what fraction of the same room can Joseph paint in 20 minutes.

1-3/x = one hour

1-3/x/3 = 20 minutes = 1/3 of one hour.

1 = x/x

x/x-3/x/3 = x-3/x/3 = x-3/3x

the answer is (C)

:-D
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Dek
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Lindsay can paint 1/x of a certain room in 20 minutes. What 01 Jun 2007, 13:17
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The OA is C
Well done
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qtip
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Lindsay can paint 1/x of a certain room in 20 minutes. What 01 Jun 2007, 17:13
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All,

I don't know why but KillerSquirrel's writeup, while excellent and efficient, wasn't intuitive for me (maybe thats why my quant isn't very good). Anyway, I used picking numbers to get to the answer like so:

let x=10

so Lindsey's rate is 1/10 in 60 min -> 3/10 in 20 min

and Joseph's rate is then 1 - 3/10 = 7/10 in 60 min or 7/30 in 20 min

Then go through the answers looking for 7/30 when x=10.

for ex:
a) 1/3(10) = 10/3 (no)
b) 3*10/30 = 3 (no)
c) *this should have included parenthesis like (x-3)/3x so (10-3)/3*10 = 7/30 (yes)
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Lindsay can paint 1/x of a certain room in 20 minutes. What 01 Jun 2007, 17:39
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Quote:
KillerSquirrel's writeup, while excellent and efficient
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Agreed. Manhattan Gmat recommends that you pick #s when there are variables in the answer choices and stem. I also overlooked ks's simplified method. Sometimes, that's what kills me on these probs. I tend to make things more difficult and fail to step back and look at the big pic. Does anyone else have this prob. I hope more prac. will resolve this ....
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Lindsay can paint 1/x of a certain room in 20 minutes. What 01 Jun 2007, 23:48
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qtip
All,

I don't know why but KillerSquirrel's writeup, while excellent and efficient, wasn't intuitive for me (maybe thats why my quant isn't very good). Anyway, I used picking numbers to get to the answer like so:

let x=10

so Lindsey's rate is 1/10 in 60 min -> 3/10 in 20 min

and Joseph's rate is then 1 - 3/10 = 7/10 in 60 min or 7/30 in 20 min

Then go through the answers looking for 7/30 when x=10.

for ex:
a) 1/3(10) = 10/3 (no)
b) 3*10/30 = 3 (no)
c) *this should have included parenthesis like (x-3)/3x so (10-3)/3*10 = 7/30 (yes)
Show more


This is a good way ! qtip - good explanation.

:-D
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Lindsay can paint 1/x of a certain room in 20 minutes. What 02 Jun 2007, 17:19
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How about this way :
Say Joseph paints 1/y of room in 20 mts

Together they paint :
1/x + 1/y of the room in 20 mts

Since they paint all of the room in 60 mts in 20 mts they paint only 1/3
so 1/x + 1/y = 1/3
1/y = 1/3-1/x
1/y = (x-3)/3x which is Answer choice 3 ?
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KillerSquirrel
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Lindsay can paint 1/x of a certain room in 20 minutes. What 02 Jun 2007, 18:50
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bsd_lover
How about this way :
Say Joseph paints 1/y of room in 20 mts

Together they paint :
1/x + 1/y of the room in 20 mts

Since they paint all of the room in 60 mts in 20 mts they paint only 1/3
so 1/x + 1/y = 1/3
1/y = 1/3-1/x
1/y = (x-3)/3x which is Answer choice 3 ?
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Yes ! good way to solve.

:-D
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menonsujith
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Lindsay can paint 1/x of a certain room in 20 minutes. What 02 Jun 2007, 20:46
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Yeah, I know this question is all solved by you guys... but here goes my 2 bit :) [same approach as bsd_lover]

1/20x + 1/20y = 1/60
1/x + 1/y = 1/3
1/y = 1/3 - 1/x
1/y = (x-1)/3x
Choice C :barbarian

Sujith



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This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
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