Bunuel wrote:

If a child is randomly selected from Columbus elementary school, what is the probability that the child will be a boy?

P(b)=\frac{b}{b+g}=?

(1) If 25 boys are removed from the school, the probability of selecting a boy will be 0.75 --> \frac{b-25}{(b-25)+g}=\frac{3}{4} --> b-3g=25. Not sufficient.

(2) There are 35 more boys than there are girls --> g=b-35. Not sufficient.

(1)+(2) We have two linear equation with two unknowns (b-3g=25 and g=b-35), thus we can solve for both and get the value of \frac{b}{b+g}. Sufficient.

Answer: C.

Hi Bunuel,

Can you please shed some light on why it would not be correct to state the following:

For the statement 1, p(girl)=(g/(b-25+g))=0.25.

Assuming this inference is correct, we can find the number of boys using a two equation,two unknowns approach.

Thank you!