These above videos explain above and beyond the idea of demand. They directly address the Law of Demand, break it apart and explain it. The videos are highly recommended if you are confused of this idea in any way. The videos are broken up into three parts. They talk about the law of demand, and the demand curve. They explain demand, and show differences between change in demand, and change in quantity demanded. The videos are good educational source.

Question 1- Person A goes to a store and buys 5 boxes of cereal for $3 each. A month later the same person goes to the store and buys only 2 boxes of cereal for $8 each. Assume no other variables have changed. This is a change in...

A) Income
B)Quantity Demanded
E)Stride Gum...Long Lasting...SPIT IT OUT or we will find you!!!!!!!!!!!
-Scroll down for answer _-_-_
Answer is ??????????????
= The question tells us that no other variables have changed, so we have to assume that income, and supply are the same. Also we have to assume no determinants of demand changed because the question states that no other variables have changed. From that we know that we have the same demand curve. And the only difference is that price rose, and thus quantity demanded dropped, according to the Law of Demand. It was movement along the same demand curve. Quantity demanded changed from 5 to 2, not the whole demand curve. Thus, the answer is B.

Helpful Websites-
Wikipedia- Demand Curve
Differences between Demand and quantity demanded
Economic Basics