A can do a piece of work in 6days, and B can do it in 5days. If C, who can do the work in 12days, joins them, how long will they take to complete the work?  Choose the correct choice from the following choices
A) 2 days	B) 3.5 days	C) 2.2 days	D) 4 days	E) 5.7 days

Rationale: a , b , and c do the work in = 6 * 5 * 12 / 6 * 5 + 5 * 12 + 6 * 12 = 360 / 162 = 2.2 days answer is c
Answer: C