One crew can drywall a house in 7 days and another crew can drywall the same house in 9 days. If both crews work together, how long will it take to dry wall the house?
A) 8 days
B) 6 days
C) $\frac { 63 } { 16 }$ days
D) $\frac { 7 } { 2 }$ days

Question

Quizplus · Accepted Answer

The first crew can complete $\frac{1}{7}$ of the house per day, and the second crew can complete $\frac{1}{9}$ of the house per day. Working together, they can complete $\frac{1}{7} + \frac{1}{9} = \frac{9}{63} + \frac{7}{63} = \frac{16}{63}$ of the house per day. Therefore, to complete the house, it would take them $\frac{63}{16}$ days.

One Crew Can Drywall a House in 7 Days and Another