arithmetic - two pipes a and b can frll a tank in 24 min and 32 min respectively if both the pipes are opened simultaneously after how much time b should be closed so that the tank is full in 18 minutes - skillgun

Let B be closed after x minutes. Then,
part filled by (A + B) in x min. + part filled by A in (18 - x) min. = 1.
X {1/24 + 1/32] + (18 – x) X 1/24 = 1 or 7x/96 + (18 – x)/24 = 1
7x + 4(18 –x) = 96 or x=8
Hence, B must be closed after 8 minutes