Question

A is twice as efficient as b, if they both complete a work in 30 days, how long will a alone take to complete the same work.

Answer 1

$\frac{1}{a} + \frac{1}{2a} = \frac{1}{30} \\ \frac{3}{2a} = \frac{1}{30} \\ 2a = 90 \\ a = \frac{90}{2} \\ a = 45$
Therefore a can complete the work in 45 days