Mike can cut a 40 foot by 20 foot yard with a push mower in 25 minutes. At this rate, how many more minutes would it take him to cut a 40 foot by 30 foot yard?
area of the yard is 40 .20 = 800sq ft time taken = 25 mins time taken to mow 1sq ft = 25/800 mins time taken to mow 40 .30 =1200sq ft = ( 25 .1200)/800 = 371/2 mins thus the extra time taken will be 371/2-25 = 121/2 mins