Bbotin D.A.

Mosmetrostroy hired two excavators to dig a tunnel. One of them can dig twice as much as the other in an hour, and they are paid the same amount per hour of work according to the contract. Which would be cheaper -
joint work of the excavators from both sides until they meet, or digging half of the tunnel by each excavator in turn?
A meter of tunnel dug by a "fast" excavator is cheaper.

## Solution

In one hour, a fast excavator digs more, but they are paid the same. Therefore, a meter of tunnel dug by a "fast" excavator is cheaper. In the "until they meet" scenario, the "fast" excavator will dig more than half of the tunnel, so it is cheaper to dig until they meet.

## Answer

Joint work.