Math World Problem 

- At one location it takes him 5 hours to cut the entire lawn using the push mower 

- it Only takes 70 minutes with the powerful riding mower 

-90% of the lawn was cut using the power full riding mower 

-the other 10% was cut using the push mower 

it takes manny 93 minutes to cut 100% of the lawn

explanation : it takes him 90% of 70 minutes (0.90*70=63 minutes ) to cut 90% of the lawn with the powerful riding mower .

But then again he only cuts 90% of the lawn with the powerful riding mower, (100% - 90% =10%) so the other 10% is done using the push mower .

Using the push mower it takes 5 hours ( 5*60=300 minutes ) to cut 100% of the lawn . so it would take him ( 0.10*300=30 minutes to cut 10% of the lawn .

then finally you say 63+30=93 . it took 93 minutes to cut the entire lawn using the powerful riding mower for 90% and the push mower for 10% of the job .