Coin Flip Puzzle

If you flip a coin 4 times, there is a 50% chance of getting a 3:1 combination—either three tails and one heads, or three heads and one tails. There is a 6/16 (37.5%) chance of two heads and two tails, and a 1/8 (12.5%) chance of all four being the same.

You can write out all 16 possible outcomes of 4 coin flips to see:

T T T T
T T T H
T T H T
T T H H
T H T T
T H T H
T H H T
T H H H
H T T T
H T T H
H T H T
H T H H
H H T T
H H T H
H H H T
H H H H

8 of these combinations are either three heads and one tails or three tails and one heads.