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# In a box there are A green balls

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CR Forum Moderator
Joined: 25 Apr 2018
Posts: 635
GMAT 1: 680 Q49 V34
In a box there are A green balls  [#permalink]

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11 Oct 2018, 10:25
00:00

Difficulty:

15% (low)

Question Stats:

78% (01:32) correct 22% (02:07) wrong based on 57 sessions

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In a box there are A green balls, 3A + 6 red balls and 2 yellow ones.
If there are no other colors, what is the probability of taking out a green or a yellow ball?

A 1/5.
B 1/2.
C 1/3.
D 1/4.
E 2/3.

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Joined: 12 Sep 2015
Posts: 4007
Re: In a box there are A green balls  [#permalink]

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11 Oct 2018, 14:47
2
Top Contributor
gmat1393 wrote:
In a box there are A green balls, 3A + 6 red balls and 2 yellow ones.
If there are no other colors, what is the probability of taking out a green or a yellow ball?

A 1/5.
B 1/2.
C 1/3.
D 1/4.
E 2/3.

Since none of the answer choices contain the variable A, we can safely assign a nice value to the value of A

If A = 1, then we have:
1 green ball
9 red balls
2 yellow balls
So, there are 12 balls altogether, and 3 of the balls are either green or yellow

So, P(selected balls is either green or yellow) = 3/12
= 1/4

Cheers.
Brent
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Re: In a box there are A green balls  [#permalink]

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11 Oct 2018, 14:52
1
Top Contributor
gmat1393 wrote:
In a box there are A green balls, 3A + 6 red balls and 2 yellow ones.
If there are no other colors, what is the probability of taking out a green or a yellow ball?

A 1/5.
B 1/2.
C 1/3.
D 1/4.
E 2/3.

We can also use algebra.

GIVEN:
A = number of green balls
3A + 6 = number of red balls
2 = number of yellow balls
TOTAL number of balls = A + (3A + 6) + 2 = 4A + 8
Number of balls that are either green or yellow = A + 2

So, P(selected balls is either green or yellow) = (A + 2)/(4A + 8)
= (1)(A + 2)/(4)(A + 2)
= 1/4

Cheers.
Brent
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Test confidently with gmatprepnow.com
Re: In a box there are A green balls   [#permalink] 11 Oct 2018, 14:52
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