Question

A man can do a piece of work in 5 days. He and his son working together can finish it in 3 days. In how many days can the son do it alone?

1. 6 ½ days
2. 7 days
3. 7 ½ days
4. 8 days

Answer 1

we know that,

Number of days man required to do piece of work = 5 days

Number of days his son required to do piece of work = 3 days

Let us consider number of days both man and his son require = x days

∴ We can calculate, work done by man in 1 hour = 1/5

Work done by his son in 1 hour = 1/x

Now, work done by both man and his son together in a 1 hour= 1/3

Now, work done by both man and his son together in 1 hour =1/5 + 1/x = x+5/5x

x+5/5x = 1/3

3x + 15 = 5x

2x =15

x = 15/2

x = 7 ½

∴ Son alone can do work together in 6 days