Supply and Demand:

P – price
Q – quantity of good
S – supply
D – demand

The four basic laws of supply and demand are:

• If demand increases and supply remains unchanged, then it leads to higher equilibrium price and higher quantity.
• If demand decreases and supply remains unchanged, then it leads to lower equilibrium price and lower quantity.
• If supply increases and demand remains unchanged, then it leads to lower equilibrium price and higher quantity.
• If supply decreases and demand remains unchanged, then it leads to higher equilibrium price and lower quantity.

Source: http://www.quicksprout.com/2012/08/16/how-to-manipulate-the-law-of-supply-and-demandand-make-a-lot-more-money/?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+Quicksprout+%28Quick+Sprout%29