How do i calculate the probability of tossing a coin 20 times and getting heads twice?

Probability of two heads or fewer is thus = (1 + 20 + 190) / 1048576 = 211/1048576 =.000201225 ... or minuscule.

Step-by-step explanation:

Number of possible outcomes after flipping a fair coin 20 times = 2^20 = 1048576. Number of ways with 0 heads = 1. Number of ways with just 1 head = 20. Number of ways with 2 heads = (20) (19) / 2! = 190.