Working alone at its constant rate, machine A produces x boxes in 10 minutes and working alone at its constant rate, machine B produces 2x boxes in 5 minutes. How many minutes does it take machines A and B, working simultaneously at their respective constant rates, to produce 3x boxes?

6 minutes

Step-by-step explanation:

Machine A produces x boxes in 10 minutes

In one minute, the machine produces x/10 boxes

Machine B produces 2x boxes in 5 minutes

In one minute, the machine produces 2x/5 boxes

Therefore in one minutes, both boxes working together will produce

= 2x/5 + x/10

=5x/10

=x/2 boxes

To produce 3x boxes, the time required

= 3x / (x/2)

= 3 * 2

= 6

It take machines A and B, working simultaneously at their respective constant rates, to produce 3x boxes in 6 minutes