 ## Probability

What is probability?
Probability is the likelihood of something happening in the future.

How is it expressed?

Probability is expressed as a fraction: the denominator is the total number of ways things can occur and the numerator is the number of things that you are hoping will occur:
```
NUMBER OF THINGS YOU ARE LOOKING FOR
PROBABILITY = ---------------------------------------
TOTAL NUMBER OF THINGS POSSIBLE
```
 Probability is always a fraction between 0 (can't happen) and 1 (will always happen)

1What is the probability of
a flipped coin turning up heads? because there is 1 head
and the coin has 2 sides.
2What is the probability of pulling,
at random, the ace of spades
out of a deck of 52 cards? because there is only 1 ace of spades and there are 52 cards in the deck.
3What is the probability of drawing
any ace out of a deck of 52 cards? because there 4 aces in a deck of 52 cards.
4What is the probability of drawing a red marble out of a bag containing 2 red marbles and 5 blue marbles? because there are 2 red marbles and 7 marbles in all.

Remember, probability is not dependent on what has happened in the past. So if you have tossed a coin and it has come up heads 6 times in a row, the probability of it coming up heads a 7th time is still just 1/2.

Now, here's a problem for you:
There are 5 marbles in a bag: 4 are blue, and 1 is red. What is the probability that a blue marble gets picked?
Probability of picking a blue marble = ______