You and your brother earned $300 mowing lawns this summer. You agreed to give your brother 1/3 of the total earnings. How much money do you owe your brother?

To find out how much money you owe your brother, you need to calculate 1/3 of the total earnings of $300.

\[ \text{Amount owed to brother} = \frac{1}{3} \times 300 = 100 \]

You owe your brother $100.