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# A box contains only white balls, red balls and green balls. What is th

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Math Expert
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A box contains only white balls, red balls and green balls. What is th  [#permalink]

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30 Mar 2015, 05:44
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A box contains only white balls, red balls and green balls. What is the probability of selecting a ball that is either red or white?

(1) The probability of selecting a white ball at random is 2/5

(2) The probability of selecting a green ball at random is 1/3

Kudos for a correct solution.

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A box contains only white balls, red balls and green balls. What is th  [#permalink]

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30 Mar 2015, 05:47
1
Had this one in my Veritas CAT (screwed up there lol).

A box contains only white balls, red balls and green balls. What is the probability of selecting a ball that is either red or white?

(1) The probability of selecting a white ball at random is 2/5

(2) The probability of selecting a green ball at random is 1/3

1) - insufficient because you don't know what the probability of either red or green is.
2) sufficient, because you know the chance of not picking red or white is 1/3, so the change of picking red or white is 2/3.

B.
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Re: A box contains only white balls, red balls and green balls. What is th  [#permalink]

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30 Mar 2015, 10:37
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Bunuel wrote:
A box contains only white balls, red balls and green balls. What is the probability of selecting a ball that is either red or white?

(1) The probability of selecting a white ball at random is 2/5

(2) The probability of selecting a green ball at random is 1/3

Kudos for a correct solution.

Our goal is to find P(red or white). Since there are only red, white, and green balls, this probability is the same as 1- P(green). So, either we need both values for P(red) and P(white)or a value for P(green).

(1) P(white) = 2/5. Not sufficient. We need P(red).

(2) P(green) = 1/3. Sufficient. We know that P(red or white) = 2/3.

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Re: A box contains only white balls, red balls and green balls. What is th  [#permalink]

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30 Mar 2015, 11:33
B. Statement 2 alone is sufficient.

1. P(W) = 2/5. This alone is not sufficient because we don't know anything about red and green ball probability.
2. P(G) = 1/3. This alone is sufficient because, probability of not drawing a green ball would be 1-P(G); and we know that the basket has only W, R and G balls. Therefore, probability of drawing a red or white ball will equal to probability of not drawing a green ball; which is equal to 1-P(G).
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Re: A box contains only white balls, red balls and green balls. What is th  [#permalink]

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31 Mar 2015, 08:08
Probability of selecting green ball = probability of selecting either white or red ball
Only B is sufficient
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Re: A box contains only white balls, red balls and green balls. What is th  [#permalink]

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31 Mar 2015, 23:06
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Probability of choosing a ball that is red or white = 1-p(green).

Statement 2 is sufficient, my answer is B.
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Posts: 56304
Re: A box contains only white balls, red balls and green balls. What is th  [#permalink]

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06 Apr 2015, 05:36
Bunuel wrote:
A box contains only white balls, red balls and green balls. What is the probability of selecting a ball that is either red or white?

(1) The probability of selecting a white ball at random is 2/5

(2) The probability of selecting a green ball at random is 1/3

Kudos for a correct solution.

MAGOOSH OFFICIAL SOLUTION:
Attachment:

selectingeitherredorwhite_text.PNG [ 16.66 KiB | Viewed 5437 times ]

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Re: A box contains only white balls, red balls and green balls. What is th  [#permalink]

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15 Jul 2018, 06:49
generis niks18 pikolo2510 amanvermagmat pushpitkc

Stumped by language in q stem.

A box contains only white balls, red balls and green balls. What is the probability of selecting a ball that is either red or white?

Quote:
(1) The probability of selecting a white ball at random is 2/5

OK, so all I need to find either probability of selecting a red ball or white ball.
Since P(white) ball is known from this option, why is this not suff.
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Re: A box contains only white balls, red balls and green balls. What is th  [#permalink]

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15 Jul 2018, 09:08
generis niks18 pikolo2510 amanvermagmat pushpitkc

Stumped by language in q stem.

A box contains only white balls, red balls and green balls. What is the probability of selecting a ball that is either red or white?

Quote:
(1) The probability of selecting a white ball at random is 2/5

OK, so all I need to find either probability of selecting a red ball or white ball.
Since P(white) ball is known from this option, why is this not suff.

Statement 1: provides only the information about white ball, but we are asked to find the probability of either red or white. So in real life the probability of selecting either of the two items from among three items will always be higher than the probability of selecting only One item. Hence Statement 1 will not give you the complete probability.

In General OR means + in probability. so here you need to add the probabilities of red and white to get the final value.
Re: A box contains only white balls, red balls and green balls. What is th   [#permalink] 15 Jul 2018, 09:08
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