pre calc
posted by kayla on .
it takes my father 3 hours to plow our cornfield with his new tractor using the old tractor it takes me 5 hours. if we both plow for 1 hour before i go to school, how long will it take dad to finish the plowing.
I got 2.5 hours but i think that is totally wrong?????

combined rate=field/3hrs + field/5hrs
time=field/(field/3 + field/5)
time= 15/(8)= less than your time.