William and Harry played 15 rounds of tic-tac-toe. William won 5 more rounds than Harry. How many rounds did William win?
Let's think step by step.
10
They played 15 rounds and William won 5 more rounds than Harry so that leaves 15 - 5 = 10 round.

There are 2 players and 10 rounds so they each won 10 / 2 = 5 rounds.

William won 5 more rounds than Harry and they each won 5 rounds so William won 5 + 5 = 10 rounds.

.

The answer is 10