Question

Bob and James are finishing the roof of a house =. Working alone, Bob can shingle the roof in 10 hours. James can shingle the roof in 16 hours. How long will it take them working together to shingle the roof? Round your answer to the nearest hundredth if necessary.

A) 13 hours
B) 26.67 hours
C) 6.15 hours
D) 0.04 hours

Answer 1

Bob can do a tenth of the roof in an hour
James can do a sixteenth in an hour

Bob can do 16/160 of the roof in an hour
James can do 10/160 of the roof in an hour

Together they do 26/160 of the roof in an hour
160/26 = 6.15 (to 2 d.p.)