Question

A does 4/5 of a piece of work in 20 days .he then callin B & they finish the remaining work in 3 days.how long B alone will take to do whole work ?

Answer 1

Given that A does 4/5 of a piece of work in 20 days .

This means for doing full work alone A requires 20(5/4) = 25 days.

Now let B takes x days to complete the work alone.

Then B can do 1/x of work in one day.

Hence in 3 days work done = work done by A + work done by B

= 3/25 +3/x = (1-4/5) = 1/5

Multiply by 25x throughout.

3x+75 = 5x

2x =75

x =37.5 days.

B alone will take37.5 days  to do whole work

Answer 2

Answer:

37.5

Step-by-step explanation:

A does 4/5 of the work in 20 days, or he would take (5/4)*20 = 25 days to do the whole work, alone.

A does (1/25)th of the work in 1 day.

A and B do (1/5)th of the work in 3 days. Or A and B, together, do (1/15)th of the work in 1 day.

So, B alone does (1/15)-(1/25) = (25–15)/(15x25) = 10/375 = 2/75th of the work in a day.

Thus, B alone will do the whole work in 37.5 days.