A man can do a piece of work in 5 days. But with the help of his Son, he can do it in three days. Son alone progress in how many days?

A) 7.5 days ✓

B) 6.5 days

C) 5.5 days

D) 4.4 days

let, man=A and son=B

A=5d and A+B=3d

B=?

we now that,

time and work are inversely propertinal

i.e: A=2 days so A’s work is 1/2

now , A=1/5 and A+B=1/3

use, A+B = A+B

1. 1/5+1/x=1/3

2. 1/x=2/15

3. 2x=15

4. x= 7 1/2 or 7.5