A, B and C are pipes attached to a cistern. A and B can fill it in 10 and 15 minutes respectively, While C can empty it in 20 minutes. If A, B and C be kept open successively for one minute each, find the last integral number of minutes required for the cistern to get filled	Pick one
A) 24 min 40 sec.	B) 24 min 30 sec.	C) 24 min 20 sec.	D) 24 min 10 sec.	E) 24 min 50 sec.
3 min filling=(1/10)+(1/15)-(1/20)=7/60   So upto   3*8= 
<gadget id="calculator">  3*8</gadget>
<output>24</output>
24th min, cistern filled=7*8/60=56/60=14/15   Remaining=1/15, which is to be filled by 'A' again   time taken by A=(1/15)/(1/10)=2/3 min.=40 sec.   So total time required=24 min+ 40 sec.   24 min 40 sec.NSWER:24 min 40 sec.
<result>A</result>
A, B and C are pipes attached to a cistern. A and B can fill it in 10 and 15 minutes respectively, While C can empty it in 20 minutes. If A, B and C be kept open successively for one minute each, find the last integral number of minutes required for the cistern to get filled