A and B can together complete a piece of work in 6 days. If A alone can complete the same work in 12 days, in how many days can B alone complete that work?

12 days

Let efficiency of A & B is = A & B

Total work = Efficiency × Time

ATQ,

(A + B) can do the work in = 6 days

Total work = (A + B) × 6  .....................(i)

A alone can do the work in = 12 days

Total work = A × 12  .....................(ii)

(i) = (ii), work is same

(A + B) × 6 = A × 12

6A + 6B = 12A

6A = 6B

A = B

Therefore,

B also can do the same work in 12 days.