Probability

Probability is about how Likely something is to occur, or how likely something is true.

The mathematic probability is a Number between 0 and 1.

0 indicates Impossibility and 1 indicates Certainty.

The Probability of an Event

The probability of an event is:

The number of ways the event can happen / The number of possible outcomes.

Probability = # of Ways / Outcomes

When tossing a coin, there are two possible outcomes:

Way	Probability
Heads	1/2 = 0.5
Tails	1/2 = 0.5

The probability of an event A is often written as P(A).

When tossing two coins, there are 4 possible outcomes:

When throwing a dice, there are 6 possible outcomes:

The possibility of throwing 3 fours at the same time is
(1/6)³ (Lands on 4 to the power of 3):

The possibility is:

let p = Math.pow(1/6, 3);

The possibility of throwing 3 likes at the same time is 6 times larger:
(lands on 1) + (Lands on 2) + ... + (Lands on 6)

The possibility is:

let p = Math.pow(1/6, 3) * 6;

I have 6 balls in a bag: 3 reds, 2 are green, and 1 is blue.

Blindfolded. What is the probability that I pick a green one?

Number of Ways it can happen are 2 (there are 2 greens).

Number of Outcomes are 6 (there are 6 balls).

Probability = Ways / Outcomes

The probability that I pick a green one is 2 out of 6: 2/6 = 0.333333.

The probability is written P(green) = 0.333333.

P(A) = P(B)	Event A and B have the same chance to occur
P(A) > P(B)	Event A has a higher chance to occur
P(A) < P(B)	Event A has a lower chance to occur

For the 6 balls:

P(red) > P(green)	I am more likely to pick a red than a green
P(red) > P(blue)	I am more likely to pick a red than a blue
P(green) > P(blue)	I am more likely to pick a green than a blue
P(blue) < P(green)	I am less likely to pick a blue than a green
P(blue) < P(red)	I am less likely to pick a blue than a red
P(green) < P(red)	I am less likely to pick a green than a red

The probability of choosing a king in a deck of cards is 4 in 52.

Number of Ways it can happen are 4 (there are 4 kings).

Number of Outcomes are 52 (there are 52 cards).

Probability = Ways / Outcomes

The probability is 4 out of 52: 4/52 = 0.076923.

The probability is written P(king) = 0.076923.