Question

Pipe a alone can fill a tank in 16 hours. Pipe b can fill it in 12 hours. If both the pipes are opened together

Answer 1

There is an simple easy trick which is

product of times ÷ sum of times

which is (16 × 12 / 16 + 12)

= 192 / 28 ≈ 6.85 hours(approx)