<u>Answer:</u>
Both Sally ans Manny can detail a car in 20.6 min.
<u>Solution: </u>
Let us assume that together they will take total x minutes to detail the car.
Sally detail the car in 50 min.
So in 1 min sally can detail \left(\frac{1}{50}\right) of the car.
Hence in x min sally can detail \left(\frac{x}{50}\right) of the car.
Manny can detail a car in 35 min.
So in 1 min many can detail \left(\frac{1}{35}\right) of the car.
Hence in x min Manny can detail \left(\frac{x}{35}\right) of the car.
So we can say,
\left(\frac{x}{50}\right)+\left(\frac{x}{35}\right)=1
x\left(\frac{1}{50}+\frac{1}{35}\right)=1
x\left(\frac{7+10}{350}\right)=1
\left(\frac{17 x}{350}\right)=1
x=\left(\frac{350}{17}\right)=20.5
8 20.6
So, both of them can detail a car in 20.6 min.