How long would two companies working together need to install the chairs if Company X can install chairs in a theater in 10 hours Company Y can install them in 15 hours?

Answer 1

Let us assume 100 chairs so as to be able to do the math.

100 chairs in 10 hours by Company X works out to ten chairs per hour or one chair every six minutes.

100 chairs in 15 hours by Company Y works out to 6 and 2/3 chairs being done per hour or one chair every nine minutes. (Actually nine minutes and change, but very, very small change.)

In 6 hours, Company X would have 60 chairs done. In the same 6 hours, Company Y would have 40 chairs done. 60 plus 40 equals 100.