If the price and quantity change in the same direction is supply or demand changing?

Answer 1

Both supply and demand must be changing, and not necessarily in the same direction. The fact that the quantity of something is changing tells you that the supply has changed. The fact that the value of something is changing in the same direction as its changing supply tells you that the demand must also be changing.

For instance; Imagine that you have 1000 pencils to sell to 1000 people for $10 per pencil (everone needs one and only one, so they will pay). If you lost half of your pencils, the supply has decreased and now stands at 500 pencils. The only way for the price of the pencils ($10 dollars each) to decrease (as did the supply/quantity), is for the number of people who want pencils (demand) to also decrease to less than 500 people. If the demand didn't change, the value of the pencils would have to rise (the opposite of what the supply did), since there would be more people who want pencils, than there are pencils to sell them.