Question 781310
The sum of their rates is the filling rate when both pumps work at the same time.

Pump A, 1/3 tanks per hour
Pump B, 1/4 tanks per hour


Pump A and B Together, {{{(1/3)+(1/4)}}} tanks per hour
{{{4/12+3/12}}}
{{{7/12}}} tanks per hour.


The other way to describe this combined rate is {{{12/7=highlight(1&5/7)}}} HOURS to fill THE TANK.