Question

If a pipe can fill a tank in 2 hrs. and
another pipe can fill the same tank in
6 hrs. then what part of a tank will be
filled by both pipes in 1 hr., if they are
opened simultaneously ?​

Answer 1

If both pipes are opened at same time, units filled per hour is 2+1 = 3 units/hr.

Thus time taken to fill 12 unit capacity of tank is 12 units/(3 units/hr) = 4 hours!

That’s your answer -> 4 hours.

Alternately, you can just use the formula 6*12/(6+12) = 72/18 = 4hrs.