The first skier started earlier than the second for 10 minutes. Distance of 30 km was first skier with an average speed of 18 km / h. The second skier was first third of the distance at 18 km / h, the second third of the distance at 20 km / h. What is the average rate of the second skier moving in the last third of the race, when skiers finished at the same time?

Detailed solution shorthand terms, formulas, laws used in the decision, the withdrawal of the calculation formula and the response.
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