Question

This equation models the number of minutes, m, it takes dave and danica to wash the dishes. m m 18 20 about how many minutes will it take them to wash the dishes?
a. 9.5 minutes
b. 9 minutes
c. 8.5 minutes
d. 38 minutes
e. none of these

Answer 1

The formula is
time = (Worker 1 * Worker 2) / (Worker 1 + Worker 2)
time = (18 * 20) / (18 + 20)
time = 360 / 38
time = 9.4736842105 minutes
So, the answer is "a. 9.5 minutes".

Source
http://www.1728.org/work.htm