70 men can complete a wall of 150 metres length in 12 days. How many men will complete the wall of length 600 metres in 30 days?

Solution: 
As the length of wall increase, the more men will be needed. so, It is a direct proportion. 
As the working days increase, the less men will be needed. It is a Inverse proportion. 
Let the numbers of men be ï½˜ then,


Here the equation will be 

`\frac{ｘ}{70}`  = `\frac{600}{150}` ï½˜ `\frac{12}{30}` 

Or

ｘ = `\frac{600}{150}` ï½˜ `\frac{12}{30}`   ï½˜ 70 Men

by simplifying we get

ｘ =  112 Men

Thus, 112 Men will be needed to construct the wall.