A is twice good a workman as B and therefore is able to finish a job in 30 days less than B. Working together they can do it in -

Question: A is twice good a workman as B and therefore is able to finish a job in 30 days less than B. Working together they can do it in -

Solution:
Let B can do the work in x days.
A can do the work in (x - 30) days.
A is twice efficient as compared to B.
(x - 30) = x/2
x = 60 days

B can do the work in 60 days while A can do the work in 30 days.

Total time taken by A and B together to complete the work = 1/(1/60 + 1/30)
= 20 days