I started 2 watches at the same time, It turned out that one of them went two minutes per hour too slow, and the other went one minute per hour too fast. When I looked at them again, the faster one was exactly one hour ahead of the other. How long had the watches been running?
Ответ: The faster watch gains on the slower one at the rate of three minutes every hour. After 20 hours, the faster one will be ahead by one hour.