Suppose we pick 3 students at random from a class with 10 boys and 15 girls. let x be the number of boys selected and y be the number of girls selected. find e (x-y

The probability of the first pick to be a boy is 10/25.

Let S be the sample space and E be the event of selecting 1 girl and 2 boys.

n (S) = number of ways selecting students of 25.

=²⁵C₃

=25·24·23/3·2·1

=2300

n (E) = (¹⁰C₁·¹⁵C₂)

=[10· (15·14) / 2·1

=10500

P (E) = n (E) / n (S) = 1050/2300=21/46