WORK RELATED PROBLEMS
Generally if a person can do the work in 'N' days means (1/N) is the work done by the person in one day.
This can be called as work rate of the person.
Work rate of Person = 1/T
where T is the numbers of days/time required to complete the given work by the given person.
The other case is if a person's one day work(Work rate) is know then the reciprocal would give the total number of days required to complete the work.
Time required = 1/one day work (work rate)
and another thing you should know if how much time will group of people take to complete the work if their individual work rates are known,this formula could be useful.
1/Ta+1/Tb+...+1/Tn=1/Tco
Where Ta,Tb,...Tn are individual time taken and Tco is combined timetaken
Note:
If A is twice good as B means
work rate of A to B is 2:1
Time taken by A and B to complete the work is 1:2