Which of the following vary directly and which vary inversely with each other and which are neither of the two?
(i) The quantity of rice and its cost.
(ii) The height of a tree and the number of years.
(iii) Increase in cost and number of shirts that can be purchased if the budget remains the same.
(iv) Area of land and its cost.
(v) Sales Tax and the amount of the bill.
i. The quantity of rice and its cost are directly proportional to each other.
e.g., If 1 kg of rice price = ₹ 40. Then, 2kg of rice price = ₹ 2 × 40 = ₹ 80.
ii. The height of a tree and the number of years is neither directly nor inversely proportional to each other.
iii. Increase in cost and number of shirts that can be purchased if the budget remains the same is inversely proportional to each other.
e.g. If 2 shirt’s prices = ₹ 800. After increase in price each price.
1 shirt price becomes of ₹ 800 where budget = ₹ 800.
iv. Area of land and its cost are directly proportional to each other.
e.g. Let 200m2 land cost = ₹ 5000
Then, 400m2 land cost = ₹ 10,000
v. Sales tax and the amount of the bill are directly proportional to each other.
e.g. Let bill amount = ₹ 1000
Sales tax = 10
Then, sales tax = 
But if, bill amount = 2000
Sales tax = 10
Then, sales tax = 