Question

One optical scanner can read a stack of sheets in 20 minutes. A second scanner can read the same stack in 12 minutes. How much time would it take for both scanners together to process the one stack of sheets?

Answer 1

• 7.5 minutes

Explanation:

First scanner can read 1/20 of all sheets in 1 minute

Second scanner can read 1/12 of all sheets in 1 minute

Both scanners can read in 1 minute:

• 1/20 + 1/12 = 3/60 + 5/60 = 8/60 = 2/15 of all sheets

Time to read all sheets:

• 1/(2/15) = 15/2 = 7.5 minutes