Jane can detail a car by herself in 50 minutes. Sally does the same job in 35 minutes. How long will it take them to detail a car working together?

Question

Write as a fraction 

Answer 1

time together + time together = 1

   time alone          time alone

Let t = the number of minutes it will take them working together

t/50 + t/35 = 1   Multiply both sides by 1750.

35t + 50t = 1750

85t = 1750

t = 20 10/17 minutes