Edmund's Brainteasers
Problem 18
Problem 18: Jonathan's walk
As we know, Jonathan walks quickly. He does 4 miles per hour on the flat, 3 miles per hour uphill, but I can't remember how fast he walks downhill. He went for a walk in the Scottish Borders, walking partly along the flat and partly uphill, returning on the same path. "I walked for 6 hours," Jonathan told me. "How far did you walk," I asked. Now Jonathan didn't know that I'd forgotten how fast he walked downhill and told me that I could work out the distance that he walked without knowing how much of the walk was on the flat and how much was on the hill. This information was enough for me to work out his speed downhill. How fast does Jonathan walk downhill? How far did he walk?