Word problem

Question

Ricky can plow a field in 15 hours. It takes Arnold 12 hours. If Ricky started at 6am and Arnold cane to help at 9am. Without any breaks, when would they finish?

Answer 1

Ricky's work rate: 1/15 of whole job can be done in 1 hour

Arnold's work rate: 1/12 of whole job per hour.

 

Together, sort of:  (t+3)(1/15) + t(1/12) = 1; this represents 100% of whole job done by two individuals working two different lengths of time, t, measured from 9 a.m.

 

Solve for t; ending time is computed by adding t to 9 a.m.