Solve the problem using an equation
Pronto Press can print an order of booklets in 4.5 hours. Red Dot printers can do the same job in 5.5 hours. How long will it take if both presses are used?
1/4.5 + 1/5.5 = 1/t
(This is the same as above but a little bit more intuitive)
Solve for t:
t/4.5 + t/5.5 = 1
t/4.5 (5.5/5.5) + t/5.5(4.5/4.5) = 1
5.5t/24.75 + 4.5t/24.75 = 1
10t/24.75 = 1
(10t/24.75)(24.75) = 1(24.75)
10t = 24.75
t = 24.75/10
t = 2.475 hours