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# A large urn contains 100 balls, of which 36% are red and the rest are

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Senior DS Moderator
Joined: 27 Oct 2017
Posts: 1138
Location: India
GPA: 3.64
WE: Business Development (Energy and Utilities)
A large urn contains 100 balls, of which 36% are red and the rest are  [#permalink]

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30 Nov 2018, 18:34
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(N/A)

Question Stats:

89% (01:22) correct 11% (01:03) wrong based on 45 sessions

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A large urn contains 100 balls, of which 36% are red and the rest are blue. How many of the blue balls must be removed so that the percentage of red balls in the urn will be 72% (No red balls are to be removed.)
A) 28
B) 32
C) 36
D) 50
E) 64

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Joined: 02 Aug 2009
Posts: 7108
Re: A large urn contains 100 balls, of which 36% are red and the rest are  [#permalink]

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30 Nov 2018, 18:45
gmatbusters wrote:
A large urn contains 100 balls, of which 36% are red and the rest are blue. How many of the blue balls must be removed so that the percentage of red balls in the urn will be 72% (No red balls are to be removed.)
A) 28
B) 32
C) 36
D) 50
E) 64

Now 36% are red means 36 are red and 100-36 or 64 are blue.

Some blue balls are removed and 36 has now become 72%.
Let the final number after removal is y..
So $$\frac{72}{100}$$y=36.....y=36*100/72=50
So the total number of balls left is 50, which means 100-50 or 50 have been removed.
As we know only blue balls have been removed, 50 blue balls must be removed..

D
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Re: A large urn contains 100 balls, of which 36% are red and the rest are  [#permalink]

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30 Nov 2018, 23:43
1
gmatbusters wrote:
A large urn contains 100 balls, of which 36% are red and the rest are blue. How many of the blue balls must be removed so that the percentage of red balls in the urn will be 72% (No red balls are to be removed.)
A) 28
B) 32
C) 36
D) 50
E) 64

This took me ~2 mins to understand the question ..

From given info total balls =100, out of which red 36 and blue 64

We have to find total of balls which would make the count of 36 red balls as 72% of the total which has to be done by removal of blue balls.

So lets find value of total balls at which 36 red balls is 72%
Let x be total balls
36/x= 0.72
solve of x we get 50 , since given that total balls are 100 and we have found that @ 50 , 36 red balls would be 72% so we would have to remove 50 out of 64 available blue balls to make the red balls @ 72%, IMO D..
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Joined: 10 Sep 2018
Posts: 45
Re: A large urn contains 100 balls, of which 36% are red and the rest are  [#permalink]

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01 Dec 2018, 02:33
36
______ X 100 = 72 ( Removing X Blue balls from total 100 balls )
100-X

Solving for x value is 50
Manager
Joined: 26 Feb 2017
Posts: 89
Location: India
GPA: 3.99
Re: A large urn contains 100 balls, of which 36% are red and the rest are  [#permalink]

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01 Dec 2018, 03:42
(36/100-X)*100 = 72
3600=7200-72X
3600 = 72X
50 = X

50 blue balls need to be removed.

Re: A large urn contains 100 balls, of which 36% are red and the rest are &nbs [#permalink] 01 Dec 2018, 03:42
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