Rs.8,000 are sufficient for a family of 4 members for 40 days. For how many days Rs.15,000 will be sufficient for a family of 5 members? 


Solution:  
According to given conditions, as the amount increases the number of days also increases. So it is direct proportion. 

As the members of a family increase the number of days decrease. So it is an inverse proportion.

According to the above proportions the vertical form of proportion will be as show below


Here the equation will be 

`\frac{ｘ}{40}`  = `\frac{4}{5}` ï½˜ `\frac{15,000}{8,000}` 

Or

ｘ = `\frac{4}{5}` ï½˜ `\frac{15,000}{8,000}`   ï½˜ 40

by simplifying we get

ｘ =  60 days

Hence, the amount will be sufficient for 60 days