Question

if A, B and C can do a work in 90, 30& 45 days respectively. if they work together, in how many days will they complete the work?

Answer 1

Number of days A, B, C can do a work = 90,30,45 .

In one day, A can do 1/90 work.
In one day, B can do 1/30 work
In one day C can do 1*45 work .

If they work together, part of work completed in a day = 1/90+1/30+1/45 = 1+3+2/90=6/90= 1/15 .

Number of days the work get completed = x.
Total number of works = 1 .

1/15*x = 1

x = 15 .

If A, B, C work together, they can complete the work in 15 days

Answer 2

one day work of a is 1/90
one day work of b is 1/45
one day work of c is 1/30 then
1 day work of a,b,c is 1/90 +1/45 +1/30 =6/90
then reciprocal of 6/90 is 90/6 is their combined no of days to do a work is 90/6 is 15 days