The rate of Sue is 1 car per hour: 1 (c/h)
then the rate of Steve is 2 (c/h) , because Steve works faster, he can wash twice the number of cars, for the same amount of time.
Thus If Steve and Sue work together, they can wash 1 + 2 = 3
(cars per hour).
That is, the rate of Steve and Sue working together, is 3 (c/h).
In the first 30 minutes, Sue washes half of the car.
The remaining half will be washed at a rate of 3 (c/h)
The main formula is Work = Time * Rate
where Work is washing (1/2)c, and rate is 3(c/h)
Time=Work/Rate = [tex] \frac{ \frac{1}{2} c}{3 \frac{c}{h} }= \frac{1}{6}h [/tex]
1/ 6 h =(1/6)*60 min = 10 min
Answer: 10 min
