Hello, emptyglasses!

You need the Binomial Probability formula . . . several times.

A fair coin was flipped 10 times.

Compute the chance that the number of heads is less than 4.

"Less than 4 heads" means: 3 heads or 2 heads or 1 head or no heads.

We must find these separate probabilities . . . andaddthem.

Therefore: .