Question

Rachael paints a room in 9 hours, Kelsey paints the same room in 15 hours Working together they can paint this room in how many hours

Answer 1

Rachael paints a room in 9 hours, so her work rate is 1/9 of work per hour.

Kelsey paints the same room in 15 hours, so her work rate is 1/15 of work per hour.

Together, their combined work rate is

$\dfrac{1}{9}+\dfrac{1}{15}=\dfrac{8}{45}$

Which means it will take them 45/8 of a hour to complete the job together.