Wilma can mow a lawn in 20 minutes. Rocky can mow the same lawn in 40 minutes. How long does it take to for both Wilma and Rocky to mow the lawn if they are working together?

Answer 1

1/20 + 1/40 = 1/T

multiply by 40T

2T + T = 40

3T = 40

T = 40/3 = 13 1/3 minutes or 13 minutes 20 seconds working together