for a fair coin, the probability of getting heads on any single toss is 1/2

six tosses, there are 2^6=64 possible outcomes

exactly 3 heads implies exactly 6-3=3 tails

ratio of total permutations to successes (exactly 3 heads and exactly 3 tails): 6!/(3!3!) = 20

(20/64) = 0.3125

0.3125 = 31.25%

There is approximately a 31% probability of getting exactly 3 heads in 6 tries