A is twice as efficient as B. Together they can do a work in 21 days. In how many days will B finish the work?
Let the number of days in which B finishes the work be ‘d’ days
Given, A is twice as efficient as B
∴ Number of days in whicha A finishes the work = d/2
Given, together they can do a work in 21 days
In 1 day, they together finish 1/21th of the work
∴ 1/d + 2/d = 1/21
⇒ 3/d = 1/21
⇒ d = 63 days