A can do a work in 7 days B in 12 days and C in 5 days. If they work on it together then in how many days required to complete the work?  Options:	A) 420/177	B) 420/179	C) 410/87	D) 90/14	E) 77/56
Person ( A ) ( 420/179 ) ( C ) (A+420/179+C)   Time - ( 7 ) ( 12 ) ( 5 )   Rate - (60) (35) ( 84 ) (179)   Work - (420) (420) (420) (420)   therefore A+420/179+C requires (420/179) days to complete entire work   = 420/179   Answer is 420/179
<result>B</result>
A can do a work in 7 days B in 12 days and C in 5 days. If they work on it together then in how many days required to complete the work?