It sounds like David ran 2 laps for every 1 lap that Carlo ran. So, for every 1 mile that Carlo ran, David ran 2 miles, which means if you add both miles together: 1 mile (Carlo) + 2 miles (David) = 3 miles, that Carlo ran 1/3 of the miles, and David ran 2/3 of the miles. In percentages, it means Carlo ran 1/3=0.333 or 33.3% and David ran 2/3=0.666 or 66.6%
