Question 564907
Albert's mowing rate = 1 lawn/40 min
Vinnie's mowing rate = 1 lawn/60 min
Working together their rate is
r = 1/40 + 1/60 [lawns/min]
r = 3/120 + 2/120 = 5/120 lawns/min
So the number of minutes per lawn is 120/5 = 24 mins.