Edmund's Brainteasers
Problem 18
Solution
Problem 18: Jonathan's walk. Solution
Since I don't need to know how much of the walk was flat and how much on a hill, then the time Jonathan takes to walk a given distance out and back on the flat must be the same as the time he takes to walk the same distance uphill out and downhill back. To walk a mile out and back on the flat takes him 30 minutes (two miles at 4 miles per hour). To walk a mile uphill takes Jonathan 20 minutes (at 3 miles per hour) so he must walk the same mile downhill on the return journey in 10 minutes. His down hill speed is therefore 6 miles per hour. He must walk a total of 24 miles, 12 out and 12 back.