We use the 10th row of Pascal’s Triangle to find the probabilities of none, one, two, three, etc heads appearing in 10 flips of a fair coin.
1 10 45 120 210 252 210 150 45 10 1 are the coefficients from row 10 and are the coefficients in the binomial expansion of (p+q)¹⁰ where p=q=½ when applied to heads and tails.
We need the fifth term 210p⁴q⁶=210/1024=0.2051 approx., being the probability of exactly 4 heads (or tails).