Question

Wilma can mow a lawn in 120 minutes. Rocky can mow the same lawn in 80 minutes. How long does it take for both Wilma and Rocky to mow the lawn if they are working together?

Answer 1

Work in the rates  / minute 
wilma:-  in 120 minutes she mows 1 lawn
             so in 1 minute she mows 1/120 lawn

similarly, Rock mows 1/80 lawn in 1 minute

working together  1/120 + 1/80  = 1/x  where x is number of minutes working together

1/20 + 1/80 =  1/48  

so 1/x = 1/48

x = 48

answer is 48 minutes