Answer and Explanation to GMAT Practice Question #8

Here is the answer and explanation to yesterday's GMAT practice question (courtesy of Integrated Learning.)

Answer: A

Explanation:
To answer this question, you can do the math, or you can rely on the experience you have gained thus far. Let’s work out statement 1 by thinking it through:

Statement 1: We know there are a specific number of girls (q). Since each number of girls would yield a different probability of choosing 2 girls, there must be only one specific number that would yield 1/11. So it must be enough information.

Now, statement 2 requires a little more thought. Let’s work it out by doing the math: Statement 2: This one may seem to follow the same logic, as they are giving us a specific probability. However, this time we are asked to pick one boy and one girl. Look at the following chart to see why this isn’t enough information:

-- Boys --	-- Girls --	---------------P(1 boy and 1 girl)* --------
1	11	1/12 x 11/11 = 1/12 x 2 = 1/6
2	10	2/12 x 10/11 = 5/33 x 2 = 10/33
3	9	3/12 x 9/11 = 9/44 x 2 = 9/22
4	8	4/12 x 8/11 = 8/33 x 2 = 16/33
5	7	5/12 x 7/11 = 35/132 x 2 = 35/66
6	6	6/12 x 6/11 = 1/4 x 2 = 1/2
7	5	7/12 x 5/11 = 35/132 x 2 = 35/66
8	4	8/12 x 4/11 = 8/33 x 2 = 16/33
9	3	9/12 x 3/11 = 9/44 x 2 = 9/22
10	2	10/12 x 2/11 = 5/33 x 2 = 10/33
11	1	11/12 x 1/11 = 1/12 x 2 = 1/6

As you can see, each probability is repeated for inverse combinations of boys and girls. There are two ways to get 16/33, once with 4 boys and 8 girls, and also with 4 girls and 8 boys. This is not enough information. We do not know what q is.

*Note: we will multiply each probability by 2, because we can choose a boy and a girl, or a girl and a boy, and both will yield the desired result.

Additional Resources:

• Integrated Learning on Facebook
• More GMAT Practice Questions
• GMAT Test Tip