Yesterday, Integrated Learning posted a 700 level GMAT question on our blog. Today, they have followed up with the answer:
Ans: A
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:
*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.
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