As can be seen from the problem, the efficiency of A and B is one in 50 and one in 40 respectively. In the case that * * * completed 20 minutes, it can be concluded that A and B completed 20 out of 50 points and 20 out of 40 points respectively, and A completed the rest alone.

Solution: Let A finish the rest of the work in X minutes.

20*50 +20*40+1/50X equals 1.

Solve x equals 5.

8 is greater than 5.

So it will not affect the normal curling.