Question

We observe both the price and quantity sold of ketchup falls over time. assuming all else stayed the same, this is due to:

Answer 1

The reason behind the falling of price and quantity of ketchup sold is that the cost of mustard seeds decreases as mustard is a substitute of ketchup and for the input mustard seeds are produced. So, if the price of mustard seed decreases, the price of ketchup also decreases.