A and B can do a piece of work in 10 days, B and C in 5 days, C and A in 15 days. How long will C take to do it?  Choices:
A) 77 days
B) 55 days
C) 12 days
D) 33 days
E) 11 days
2c = 1/5 + 1/15 – 1/10 = 1/6   c = 1/12 =&gt; 12 days   Answer: 12 days
<result>C</result>
A and B can do a piece of work in 10 days, B and C in 5 days, C and A in 15 days. How long will C take to do it?