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In a certain class, one student is to be selected at random

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

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New post 23 Jul 2012, 03:46
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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.
(2) Ten of the students in the class are girls.

Practice Questions
Question: 3
Page: 275
Difficulty: 550
[Reveal] Spoiler: OA

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

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New post 27 Jul 2012, 06:53
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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.

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

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

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New post 23 Jan 2016, 22:45
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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.
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Re: In a certain class, one student is to be selected at random [#permalink]

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New post 22 Jul 2016, 10:45
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.


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

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

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

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New post 02 Sep 2017, 06:30
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.


It's safe to assume that a student can read...
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Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


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

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New post 02 Sep 2017, 06:38
Thanks Bunuel for the answer!

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 :-D

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.


It's safe to assume that a student can read...

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

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New post 02 Sep 2017, 07:36
Ans is A

1)Let 6x students , then 4x boys
selecting 1 boy out of 4x = 4x and out of 6x is 6x
so P = 4x/6x = 2/3 , Sufficient


2)total number of girls = 10 , insufficient as number of boys are unknown. D eliminated
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In a certain class, one student is to be selected at random [#permalink]

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New post 02 Sep 2017, 10:53
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



Two-thirds of the students in the class are boys. S1 gives the desired outcome/total possibilities as 2/3. So clearly sufficient.

Statement 2 gives no clue abt the total students or the number of boys. Insufficient.

Ans:A

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In a certain class, one student is to be selected at random   [#permalink] 02 Sep 2017, 10:53
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