1.  A can do a piece of work in 4 hours; B and C together can do it in 3 hours, while A and C together can do it in 2 hours. How long will B alone take to do it?
A. 8 hours
B. 10 hours
C. 12 hours
D. 24 hours

Answer: Option C

Explanation:

A's 1 hour's work = 1 ;
4

(B + C)'s 1 hour's work = 1 ;
3

(A + C)'s 1 hour's work = 1 .
2

(A + B + C)'s 1 hour's work = ( 1 + 1 ) = 7 .
4 3 12

B's 1 hour's work = ( 7 - 1 ) = 1 .
12 2 12

Therefore B alone will take 12 hours to do the work.