siddhans 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

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 which is 2/3 <--- probability ?

So shouldn't D be correct since we can find out probabilities from 1 and 2 both individually ?? Please explain

When using statement 2, please ignore everything from statement 1. Statement 2 should prove its sufficiency independent of statement 1 to be considered independently sufficient.

For D to be correct, each of the statements should prove its sufficiency independently.

You used information from the first to find the number of students.

I see so when will C ever be an answer choice? When can we say that both the choices work together to get to an answer ?