Question

Michael can wash and detail his car in 3 hours, and Jeanne can wash and detail her car in 5 hours. If they work together, how long will it take them to wash and detail both cars?


What is the y coordinate of the y−intercept of the line that passes through the points
(−4, −1) and (4, 5)?

Answer 1

Michael washes 1/3 car per hour. In x hours he washes x/3 of the car.
Jeanne washes 1/5 car per hour. In x hours she washes x/5 of the car
In x hours, together they was x/3 + x/5 cars and they are going to wash 2 entire cars. So:
\[\frac{x}{3}+\frac{x}{5}=2\]