Question 726340
In this problem filling the tank is 1 job

Pump A takes 18 hours.
so it does 1/18 of the job in 1 hour

similarly Pump B does 1/24 of the job in 1hour

together they do {{{1/18 + 1/24 }}} of the job in 1 hour

=7/72 of the job in 1 hour

so they will take 72/7 hours to do the job together

10.38 hours