Tapas works twice as fast as Mihir. If both of them together complete a work in 12 days, Tapas alone can complete it in ?

	Tapas	:	Mihir
Efficiency units/day	2	:	1

$$\eqalign{ & {\text{T}} + {\text{M complete in 12 days}} \cr & {\text{Total work }} \cr & = 12 \times \left( {2 + 1} \right) \cr & = 36{\text{units}} \cr} $$
Tapas alone complete the whole work in
$$\eqalign{ & = \frac{{36}}{2} \cr & = 18{\text{ days}} \cr} $$