Question

It takes one machine 25 minutes to pick a bale of cotton and another machine 30 minutes to compete the same job. If both machines are used, how long will it take them to pick a bale of cotton?

Answer 1

13.64 minutes

Explanation:

The first machine works at the rate x = 1 bale/ 25 min.

The second machine works at the rate y = 1 bale/30 min.

The combined rate is

x + y = 1/25 + 1/30 bales/min

= (30 + 25)/(25*30) = 55/750

= 11/150 bales/min

The time for both machines to pick 1 bale of cotton is

(1 bale)/(11/150 bales/min) = 150/11 min = 13.64 min

So if you take rsm, you have to input 13.64 otherwise it won't work. :)