I pulled this one out of The Moscow Puzzles.
Jack London's Journey
Jack London tells how he raced from Skagway in a sled pulled by 5 huskies to reach the camp where a comrade was dying.
For 24 hours the huskies pulled the sled at full speed. Then 2 dogs ran off with a pack of wolves. London, left with 3 dogs, was slowed down proportionally. He reached camp 48 hours later than he had planned. If the runaway huskies had stayed in harness for 50 more miles, London writes, he would have been only 24 hours late. How far is the camp from Skagway?