PROBLEM 1-9-1

An auger can move a pile of grain in 30 minutes. A second auger can move the grain in 50 minutes. A third auger can move the grain in 20 minutes. If all three are used, how long will it take to move the grain?  (Give your answer in minutes and seconds).

SOLUTION 1-9-2

The first auger can move 1/30 of the grain in a minute; the second 1/50, and the third 1/20.

 1/30 + 1/50 + 1/20 = 31/300 in 1 minute

If 31/300 moved in 1 minute; then to get 300/300 moved:

1 divided by 31/300 = 9  21/31 minutes

9 minutes 41 seconds