A family has 4 children. Assuming that boys and girls are equally likely, calculate the probability, using fractions, and Bernoulli's formula (please use this specific formula when necessary)

Probability that:

(i) there are exactly 2 boys.

(ii) there are exactly 3 girls.

(iii) there is at least one boy.

As far as I know, 'k' means the number of successes, 'n' is the number of Bernoulli trials, while P is the probability, hope i am right.

Any input will do >_< Thanks...