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Probability
How Likely
In the real world, events can not be predicted with 100% certainty. The best we can do is say how likely they are to happen, using the concept of probability.

Tossing a Coin
When a coin is tossed, there are two possible outcomes:
We say that the probability of the coin landing H is 1/2.
Similarly, the probability of the coin landing T is 1/2. 

Throwing Dice
When a single die is thrown, there are six possible outcomes: 1, 2, 3, 4, 5, 6.
The probability of throwing any one of these numbers is 1/6. 
Probability
In general:
Probability of an event happening = 

Number of ways it can happen 

Total number of outcomes 
Example: there are 5 marbles in a bag: 3 are red, and 2 are blue. What is the probability that a blue marble will be picked?
Number of ways it can happen: 2 (ther are 2 blues)
Total number of outcomes: 5 (there are 5 marbles in total)
So the probability is 2/5 = 0.4


