20 Miles

A redhead, a brunette, and a blonde were shipwrecked on an island. The island was 20 miles from the main land. They had no food and no clean water, so they decided to try to swim the distance.

The redhead went first, and swam 5 miles before getting tired and drowning.

The brunette went next and managed to get 10 miles out, but then became exhausted and drowned also.

Finally, the blonde makes her attempt. She swims out 19 miles towards the mainland and then gets tired, so she swims back to the island to rest.