[ Motion Problems ]

A "Moskvich" car was sent from the post office to the airfield to transport the mail. The plane with the mail landed earlier than the scheduled time, and the mail was sent to the post office on a passing truck. After 30 minutes of driving, the truck met the "Moskvich" on the road, which took the mail and turned back without stopping. The "Moskvich" arrived at the post office 20 minutes earlier than usual. How many minutes earlier than the scheduled time did the plane land?

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How many minutes before the scheduled landing time did the "Moskvich" car meet the truck on the road?

## Solution

Since the "Moskvich" spent 20 minutes less on the entire trip (there and back), it spent 10 minutes less on the one-way trip. Therefore, the "Moskvich" met the truck 10 minutes before the scheduled landing time of the airplane. The airplane, however, landed 30 minutes before the "Moskvich" met the truck, which means it landed 40 minutes earlier than the scheduled time.

## Answer

40 minutes.