Work from Days:
If A can do a piece of work in n days, then A’s 1 day’s work = 1/n
Days from Work:
If A’s 1 day’s work = 1/n
then A can finish the work in n days.
If A is thrice as good a workman as B, then:
Ratio of work done by A and B = 3 : 1.
Ratio of times taken by A and B to finish a work = 1 : 3.
A can do a work in 15 days and B in 20 days. If they work on it together for 4 days, then the fraction of the work that is left is :