A and B can do a piece of work in 48 days, A and C can do it in 60 days, b and c can do it 72 days. In what time can c alone do it?
Choices:	A) 84 days	B) 84 ½ days	C) 85 days	D) 87 days	E) 89 days

Rationale: explanation : ( a + b ) 1 day work = 1 / 48 ( b + c ) 1 day work = 1 / 72 ( a + c ) 1 day work = 1 / 60 by adding 2 ( a + b + c ) = 1 / 48 + 1 / 72 + 1 / 60 = 37 / 720 ( a + b + c ) 1 day work = 37 / 1440 a 1 day work = 37 / 1440 – 1 / 72 = 17 / 1440 = 85 days ( approximately ) answer : option c
Answer: C