if 1000 articles of a given type can be returned out by a first machine in 8 hours, by a second in 5 hours, and by the third in 4 hours, how long will it take to turn out the articles with an machine working?

Answer 1

The machines turn our articles at rates 1000/8, 1000/5 and 1000/4 per hour.
Total production rate by all
= 125 + 200 + 250 = 575 articles/hour

575 * t = 1000
t = 1.74 hours