Tap A can fill a tank in 4 hours whereas tap B and tap C can empty in 12 hours and 16 hours respectively...

Question

Tap A can fill a tank in 4 hours whereas tap B and tap C can empty it in respectively 12 hours and 16 hours separately. All the 3 tap are opened with tank empty. After 2 hours tap B is closed, after how much time of closing of B, tank will be filled completely.

Answer 1

Considering the unit work here
part filled in 2 hours=2*[(1/4) - (1/12) -(1/16)] = 5/24

==== remaining part = 1-5/24 = 19/24

net part filled in 1 hour will be(with tank B closed) =[(1/4) - (1/16)]=3/16

=== 3/16 part == 1hour

==== 19/24 part == (16/3)*(19/24) = 38/9 = 4.22 hrs