Solution: If the total project amount is 1, then Party A will complete 1/a every day and Party B will complete 1/b every day, so the number of days required for simultaneous construction of two teams is
1/[( 1/a)+( 1/b)]=(a×b)/a+b)
The distance from port A to port B is S. If the speed of a ship from port A to port B is U 1 and the speed of returning from port B to port A is U2, what is the average speed of the ship?
According to the meaning of the question, the time for a ship to sail from Port A to Port B is S/U 1, and the time for the port to return to Port A is S/U2, so the average speed is
2S/[(S/U 1)+(S/U2)]
=2(U 1×U2)/(Ui+U2)