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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.

pair of dice

Tossing a Coin 

When a coin is tossed, there are two possible outcomes:

  • heads (H) and
  • tails (T).

We say that the probability of the coin landing H is 1/2.

Similarly, the probability of the coin landing T is 1/2.

 

pair of dice

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