Question

A man can do piece of work in 5 days, but with help of his son, he can do it in 3days. In what time can the son do it alone

Answer 1

Answer:

son can do the work in 7 days

Answer 2

Answer:

7 1/2 days

Step-by-step explanation:

let son alone can do it in x days

if they work together

(man + son)'s 1 day's work = 1/3

1/5 + 1/x = 1/3

1/x = 1/3 - 1/5 => 1/x = 2/15

x = 15/2 = 7 1/2 days

2nd method,

M => 5 ,M + S=> 3

total work = L.C.M(5,3) = 15 units

M's efficiency = 15/5 = 3 units/day

(M + S)'s efficiency=15/3 = 5 units/ day

S 's efficiency = 5 - 3 = 2 units/day

son alone can do it in = 15/2

= 7 1/2 days