A and B can finish a work together in 12 days, and B and C together in 16 days. If A alone works for 5 days and then B alone continues for 7 days, then remaining work is done by C in 13 days. In how many days can C alone finish the complete work?  Choose the correct choice from the following choices:
A) 22 days
B) 21 days
C) 25 days
D) 24 days
E) 23 days
Here LCM of 12 and 16 is taken as total work. ( becomes easy to solve)   Assume total work =48 units   Then workdone by (A+B) in one day = 48/12= 
<gadget id="calculator">48/12</gadget>
<output>4</output>
4 units   Similarly, by (B+C) in one day= 48/16= 
<gadget id="calculator">48/16</gadget>
<output>3</output>
3 units   Now according to question,   A works 5 days , B for 7 days and C for 13 days to complete total work   So, 5A + 7B + 13C= 48 units   5(A+B) + 2(B+C) + 11C = 48 units   5*4 + 2*3 +11C =48 units   11C = 22 units   C = 2 units ( C does 2 units of work daily)   Therefore, 48/2 = 24 days   C requires 24 days to complete the work alone.   Answer 24 days
<result>D</result>
A and B can finish a work together in 12 days, and B and C together in 16 days. If A alone works for 5 days and then B alone continues for 7 days, then remaining work is done by C in 13 days. In how many days can C alone finish the complete work?