Question

a and b can finish a work in 20 days .a alone can do 1/5yh of work in 12 days .in how many days can b alone do it ???

Answer 1

If a alone does 1/5 work in 12 days so he will do the 2/5 in 25, 3/5 in 36, 4/5 in 48 and 5/5 in 60 days or you can directly do reverse of 1/5 and multiply it with days that means 12×5 = 60 days

Now we got that A can do a work in 60 days and given is A and B can finish that work in 12 days if they work together..
Now
If a does whole work in 60 days so he will do 1/60 work in 1 day and A+B will do 1/20 in a day

Now if we less A's 1 day work from A+B's 1 day work then we will get B's 1 day work

So 1/20 - 1/60 = (3-1)/60

So B's one day work is 2/60 so If b does 2/60 work in a day then total time he will take to complete that work is 60/2 = 30 Days.