Susies sorority has two printers on which she can print out

Susies sorority has two printers on which she can print out pictures from their latest function. The larger printer can print all of the pictures in 3 hours, while it would take 5 hours on the smalle printer. How long would it take her to print the pictures using both printers?

Solution

pictures printed in 1 hour on larger printer= 1/3

pictures printed in 1 hour on small printer=1/5

Both printers print in 1 hour = 1/3 +1/5 = (5+3)/15 = 8/15

time taken by both printers = 15/8

that is

1.875 hours

or 1 hour and 52.5 minutes