If the fare of 12 quintal luggage for a distance of 18 km is 12 rupees, how much fare will be charged for a luggage of 9 quintals for a distance of 20 km? 

Solution: 
As the quintal luggage decrease, the fare will decrease. so, It is a direct proportion. 
As the distance increase, the fare will also increases. It is also a direct proportion. 
Let the numbers of men be ï½˜ then,


Here the equation will be 

`\frac{ｘ}{12}`  = `\frac{9}{12}` ï½˜ `\frac{20}{18}` 

Or

ｘ = `\frac{9}{12}` ï½˜ `\frac{20}{18}`    ï½˜ 12 Rs.

by simplifying we get

ｘ =  10 Rs.
Thus, Rs. 10 fare will be charged.