A works twice as fast as B. If B can complete a work in 12 days independently, the number of days in which A and B can together finish the work in :
4 days
6 days
8 days
18 days
Explanation:
Ratio of rates of working of A and B = 2 : 1.
So, ratio of times taken = 1 : 2.
Bs 1 days work =$ \dfrac{1}{12} $.
As 1 days work =$ \dfrac{1}{6} $; [2 times of Bs work]
$\left(A + B\right)$s 1 days work =$ \left(\dfrac{1}{6} +\dfrac{1}{12} \right) $=$ \dfrac{3}{12} $=$ \dfrac{1}{4} $.
So, A and B together can finish the work in 4 days.