PROBABILITY
How likely something is to happen.
How likely something is to happen.
Many events can't be predicted with total certainty. The best we can say is how likely they are to happen, using the idea 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 ½.
And the probability of the coin landing T is ½.
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 | Throwing Dice
When a single die is thrown, there are six possible outcomes:1, 2, 3, 4, 5, 6.
The probability of any one of them is 1/6.
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Probability
In general:
Probability of an event happening = Number of ways it can happenTotal number of outcomes
EXAMPLES:
Probability Line
We can show probability on a Probability Line:
Probability is always between 0 and 1
Probability is Just a Guide
Probability does not tell us exactly what will happen, it is just a guide
Example: toss a coin 100 times, how many Heads will come up?
Probability says that heads have a ½ chance, so we can expect 50 Heads.
But when we actually try it we might get 48 heads, or 55 heads ... or anything really, but in most cases it will be a number near 50.
Example 1:
The chances of rolling a "4" with a dice:Number of ways it can happen: 1 (there is only 1 face with a "4" on it)
Total number of outcomes: 6 (there are 6 faces altogether)
So the probability = 16
Example 2:
There are 5 marbles in a bag: 4 are blue, and 1 is red. What is the probability that a blue marble gets picked?
Number of ways it can happen: 4 (there are 4 blues)
Total number of outcomes: 5 (there are 5 marbles in total)
So the probability = 45 = 0.8
There are 5 marbles in a bag: 4 are blue, and 1 is red. What is the probability that a blue marble gets picked?
Number of ways it can happen: 4 (there are 4 blues)
Total number of outcomes: 5 (there are 5 marbles in total)
So the probability = 45 = 0.8
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