Ashley is twice as good as Jake and together they complete a piece of work in 20 days. In how many days will Ashley alone finish the work?
Let Jake can finish the piece of work alone in x days.
∴ Ashley can alone finish the work in x/2 days.
In 1 day Jake can do work = 1/x
In 1 day Ashley can do work = 1/(x/2) = 2/x
1/x + 2/x = 1/20
⇒ 3/x = 1/20
⇒ x = 60
∴ Ashley alone can finish the work in 60/2 i.e. 30 days