In jar A there are 3 white balls and 2 green ones...

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BTGmoderatorLU: Moderator; Posts: 2505; Joined: Sun Oct 15, 2017 1:50 pm; Followed by:6 members

In jar A there are 3 white balls and 2 green ones...

by BTGmoderatorLU » Tue Nov 14, 2017 7:19 pm

In jar A there are 3 white balls and 2 green ones, in jar B there is one white ball and three green ones. A jar is a randomly picked, what is the probability of picking up a white ball out of jar A?

A. 2/5.
B. 3/5.
C. 3/10.
D. 3/4
E. 2/3.

The OA is C.

I'm really confused with this PS question. Please, can any expert assist me with it? Thanks in advanced.

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Source: Beat The GMAT — Problem Solving | Tue Nov 14, 2017 7:19 pm

GMATGuruNY: GMAT Instructor; Posts: 15539; Joined: Tue May 25, 2010 12:04 pm; Location: New York, NY; Thanked: 13060 times; Followed by:1906 members; GMAT Score:790

by GMATGuruNY » Tue Nov 14, 2017 8:08 pm

LUANDATO wrote:In jar A there are 3 white balls and 2 green ones, in jar B there is one white ball and three green ones. A jar is a randomly picked, what is the probability of picking up a white ball out of jar A?

A. 2/5.
B. 3/5.
C. 3/10.
D. 3/4
E. 2/3.

Generally:
AND means MULTIPLY.
OR means ADD.

P(picking Jar A) = 1/2. (Of the 2 jars, one is A.)
P(selecting a white marble from A) = 3/5. (Of the 5 marbles in A, 3 are white.)
Since we want to pick Jar A and select a white marble from A, we MULTIPLY the probabilities:
1/2 * 3/5 = 3/10.

The correct answer is C.

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EconomistGMATTutor: GMAT Instructor; Posts: 555; Joined: Wed Oct 04, 2017 4:18 pm; Thanked: 180 times; Followed by:12 members

by EconomistGMATTutor » Wed Nov 15, 2017 11:08 am

In jar A there are 3 white balls and 2 green ones, in jar B there is one white ball and three green ones. A jar is a randomly picked, what is the probability of picking up a white ball out of jar A?

A. 2/5.
B. 3/5.
C. 3/10.
D. 3/4
E. 2/3.

The OA is C.

Hi LUANDATO,
Let's take a look at your question.
There are two jars A and B.
Jar A has 3 white balls and 2 green ones.
Jar B has one white ball and three green ones

P(Picking up a white ball out of jar A) = P(selecting Jar A) * P(Picking white ball from Jar A)
$$=\frac{1}{2}\times\frac{3}{5}$$
$$=\frac{3}{10}$$

Therefore, Option C is correct.
Hope it helps.
I am available if you'd like any follow up.

GMAT Prep From The Economist
We offer 70+ point score improvement money back guarantee.
Our average student improves 98 points.

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Scott@TargetTestPrep: GMAT Instructor; Posts: 8086; Joined: Sat Apr 25, 2015 10:56 am; Location: Los Angeles, CA; Thanked: 43 times; Followed by:29 members

by Scott@TargetTestPrep » Wed Oct 16, 2019 6:12 pm

BTGmoderatorLU wrote:In jar A there are 3 white balls and 2 green ones, in jar B there is one white ball and three green ones. A jar is a randomly picked, what is the probability of picking up a white ball out of jar A?

A. 2/5.
B. 3/5.
C. 3/10.
D. 3/4
E. 2/3.

The OA is C.

I'm really confused with this PS question. Please, can any expert assist me with it? Thanks in advanced.

The probability of selecting jar A is 1/2.

The probability of selecting a white ball from jar A is 3/5.

Thus, the overall probability is 1/2 x 3/5 = 3/10.

Answer: C

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