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In a certain class, one student is to be selected at random to read. What is the probability that a boy will read?

(1) Two-thirds of the students in the class are boys. Directly gives us the probability of selecting a boy. Sufficient. (2) Ten of the students in the class are girls. Clearly insufficient.

Re: In a certain class, one student is to be selected at random [#permalink]

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23 Jan 2016, 09:35

Bunuel wrote:

In a certain class, one student is to be selected at random to read. What is the probability that a boy will read?

(1) Two-thirds of the students in the class are boys. (2) Ten of the students in the class are girls.

Practice Questions Question: 3 Page: 275 Difficulty: 550

Let B is the number of Boys and G is the number of Girls. Probability that Boy will read is (B)/(B+G)

Statement 1. If number of B is 2/3 of (B+G) then number of Girls is 1/3. Substitute in to formula and get direct answer Statement 2. We don't know anything about number of Boys. Not sufficient
_________________

Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.

In a certain class, one student is to be selected at random to read. What is the probability that a boy will read?

(1) Two-thirds of the students in the class are boys. (2) Ten of the students in the class are girls.

In general, when one con is number and the other con is ratio, it is most likely that ratio is an answer. Also, since fraction=proability, que:probability and in 1) 2/3:fraction. Therefore, the answer is A.

-> from con 1) and con 2), if one of the conditions is given by numbers and the other is given by ratio (percent,fraction), then the condition with ratio (percent,fraction) value has higher chance of being the answer.
_________________

In a certain class, one student is to be selected at random to read. What is the probability that a boy will read?

(1) Two-thirds of the students in the class are boys. (2) Ten of the students in the class are girls.

We need to determine the probability that a boy will be selected to read, in a class of boys and girls.

Statement One Alone:

Two-thirds of the students in the class are boys.

Since we know that 2/3 of the class are boys, we know that the probability of randomly selecting a boy to read is 2/3. Statement one alone is sufficient to answer the question. We can eliminate answer choices B, C, and E.

Statement Two Alone:

Ten of the students in the class are girls.

Without knowing the number of boys in the class, we cannot determine the probability that a boy will be selected to read. Statement two alone is not sufficient to answer the question.

Answer: A
_________________

Jeffery Miller Head of GMAT Instruction

GMAT Quant Self-Study Course 500+ lessons 3000+ practice problems 800+ HD solutions

In a certain class, one student is to be selected at random [#permalink]

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02 Sep 2017, 06:19

Hi!

This may sound stupid to ask, but are we not assuming that the student we pick can read? I mean, I could not see anywhere in the stem that says the student we pick is capable of reading.
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My Best is yet to come!

Last edited by susheelh on 02 Sep 2017, 07:19, edited 1 time in total.

This may sound stupid to ask, but are we not assuming that the student we pick can read? I mean, I could not see anywhere in the stem that every student we pick is capable of reading.

It's safe to assume that a student can read...
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Its just that this is a DS question. I marked it as E since I thought some of the students can't read. Maybe this happened since I have a young son whom I am still not able to teach how to read

I get it now. Its safe to assume everyone can read.

Bunuel wrote:

susheelh wrote:

Hi!

This may sound stupid to ask, but are we not assuming that the student we pick can read? I mean, I could not see anywhere in the stem that every student we pick is capable of reading.