If 15 laboures earn Rs. 67,500 in 9 days, how much money will 10 laboures earn in 12 days? 

Solution: 
We see that as the number of labourers decrease, the amount of earning will also decrease. It is a direct proportion. 
As the working days increase, the amount of earning will also increase. It is also a direct proportion. 
Let the earning amount be ï½˜ Rs.


Here the equation will be 

`\frac{ｘ}{67,500}`  = `\frac{12}{9}` ï½˜ `\frac{12}{15}` 

Or

ｘ = `\frac{12}{9}` ï½˜ `\frac{12}{15}`  ï½˜ 67,500 Rs.

by simplifying we get

ｘ =  72,000 Rs.

Thus, Rs. 72,000 will be earned