Problema Solution
It takes my father 3 h to plow our cornfield with his new tractor. Using the old tractor it takes me 5 h. If we both plow for 1 h before I go to school, how long will it take him to finish the plowing?
Answer provided by our tutors
The new tractor will do 1/3 of the cornfield in 1 hour, and the old one will do 1/5 of the cornfield. 1/3 + 1/5 = 5/15 + 3/15 = 8/15 of the cornfield done in one hour. That leaves 7/15 to finish, which is 1/3 * 7/5. It will take 7/5 hours for him to finish.