1/ 12×7+( 1/ 12- 1/20)x = 1

7/ 12+ 1/30x= 1

1/30x=5/ 12

X= 12.5 The answer takes 12.5 days to complete.

Arithmetic method: As it takes 20 days for Party A to complete the project alone, Party A completes the project 1 every day. Because Party A and Party B can complete the project within 12 days, Party A and Party B * * subtract 65438 from 12 1 1 of 12. Then 1 minus 12 times 1 times 7 divided by 30 times 1 equals 12.5 days.