A and B can together finish a piece of work in 30 days. They worked on it 20 days and then B left. The remaining work was done by A alone in 20 days. A alone can finish the work in = ?

Solution(By Examveda Team)

	(T.W.) 60
2 units/day	↓
	30 days (A + B)

$$\eqalign{ & \left( {{\text{A }} + {\text{ B}}} \right){\text{ worked for 20 days}} \cr & {\text{So, they completed}} \cr & 20 \times 2 = 40{\text{ units}} \cr & {\text{Work left}} = 60 - 40 = {\text{20 units}} \cr} $$

	(T.W.) 2 0
1 units/day	↓
	20 days (A)

A's efficiency 1 units/day A will complete the whole work in
$$\eqalign{ & = \frac{{{\text{Total work}}}}{{{\text{Efficiency}}}} \cr & = \frac{{60}}{1} \cr & = 60{\text{ days}} \cr & \cr & {\bf{Alternate:}} \cr & \left( {{\text{A}} + {\text{B}}} \right) \times {\text{10}} = {\text{A}} \times {\text{20}} \cr & \frac{{{\text{A + B}}}}{{\text{A}}} = \frac{2}{1} \cr & {\text{Total work}} \cr & = 2 \times 30 \cr & = {\text{60 units}} \cr & {\text{Time taken by A alone}} \cr & = \frac{{60}}{1} \cr & = 60{\text{ days}} \cr} $$