In a certain class, one student is to be selected at random to read. what's the probability that a boy will read.
(1) Two-thirds or the students in the class are boys
(2) Ten of the students in the class are girls
The answer is A (first statement alone is sufficient). Why?
Thanks.
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In a certain class, one student is to be selected at random.
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papgust
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(1) 2/3 are boys and 1/3 are girls.
Whenever you have fractions like this, this is sufficient to answer probability.
Let's say class strength is 100, Boys are 66 and girls are 34. Probability that a boy will read is 66/100 = 2/3 approx.
OR
Let's say class strength is 48, Boys are 32 and girls are 16. Probability that a boy will read is 32/48 = 2/3.
Probability will always be same whatever numbers you plug in for this ratio. So, when you have ratios such as this, it will be sufficient to answer.
(2) I guess you are comfortable why (2) is insufficient.
Whenever you have fractions like this, this is sufficient to answer probability.
Let's say class strength is 100, Boys are 66 and girls are 34. Probability that a boy will read is 66/100 = 2/3 approx.
OR
Let's say class strength is 48, Boys are 32 and girls are 16. Probability that a boy will read is 32/48 = 2/3.
Probability will always be same whatever numbers you plug in for this ratio. So, when you have ratios such as this, it will be sufficient to answer.
(2) I guess you are comfortable why (2) is insufficient.
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kstv
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In a certain class, one student is to be selected at random to read. what's the probability that a boy will read.
(1) Two-thirds or the students in the class are boys
(2) Ten of the students in the class are girls
Probability of an event= Possible ways the event can happen/ Total possibility
To choose a boy we need to know how many boys are there and class size. Mind you the ratio will do.
2/3 say that if the class size is 3 no of boys are 2. Sufficient.
(2) No of boys known, but class size not known. Insufficient.
(1) Two-thirds or the students in the class are boys
(2) Ten of the students in the class are girls
Probability of an event= Possible ways the event can happen/ Total possibility
To choose a boy we need to know how many boys are there and class size. Mind you the ratio will do.
2/3 say that if the class size is 3 no of boys are 2. Sufficient.
(2) No of boys known, but class size not known. Insufficient.
In second case we know the number of girls are 10 . So can we not find out the number of boys ? which will be 2/3 * 10 = 20 . SO total class is of size 30 and probability that a boy will read is 20/30 = 2/3 ?
Isnt it ? So C should be correct ?? Please explain
Isnt it ? So C should be correct ?? Please explain
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SoCan
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Be careful not to include information from statement 1 when you're evaluating statement 2 on its own. The question stem does not give any information on the size or gender mix. Statement 2 only states that there are 10 girls. You don't have any information about the boys.siddhans wrote:In second case we know the number of girls are 10 . So can we not find out the number of boys ? which will be 2/3 * 10 = 20 . SO total class is of size 30 and probability that a boy will read is 20/30 = 2/3 ?
Isnt it ? So C should be correct ?? Please explain
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SoCan
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You should review the basics of DS questions. Do you have the OG or any other prep materials?siddhans wrote:But how will C ever be an answer choice then? When do we evaluate both the choices together to find an answer? I am confused
thanks everyoneGMAT/MBA Expert
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Jeff@TargetTestPrep
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We need to determine the probability that a boy will be selected to read, in a class of boys and girls.TheGuest wrote:In a certain class, one student is to be selected at random to read. what's the probability that a boy will read.
(1) Two-thirds or the students in the class are boys
(2) Ten of the students in the class are 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.
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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