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

Btw, Moved to Data Sufficiency folder

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.

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

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

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.

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

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

You should review the basics of DS questions. Do you have the OG or any other prep materials?

Yes, i do...

siddhans wrote:Yes, i do...

I would review that section. This tree is pretty helpful

Thanks i reviewed and practiced some questions and got the hang of it now thanks everyone

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

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.
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