Two pipes A and Y can fill a cistern in 24 min. and 32 min
Answer: (b) 8 min
Let B be closed after X min.
then , part filled by (A+B) in X min. + part filled by A in (18-X)min.=1
Therefore, X x ((1/24)+(1/32))+(18-x) x (1/24)=1 6 (7 X/96) + ((18-X)/24)=1.
ó7 X +4 x (18-X)=96.
Hence, be must be closed after 8 min.