A is twice as efficient as B and together, they finish a piece of work in 20 days. A alone can finish the work in:

Correct option is B

Given: 

A is twice as efficient as B 

Time taken by A + B = 20 days

Formula Used:​

Total work = Efficiency $$\times$$ Time

Solution: 

From the condition; 

Efficiency ratio;

​$$\frac{A}{B} = \frac{2}{1}$$ 

Now , total work

Total work = 3 $$\times$$ 20 = 60

time taken by A alone 

= $$\frac{60}{2} = 30 \ days$$ ​