Mathematics chapter 7 - probability

• Mathematics chapter 7 - probability

• 1 - Definition

• • Probability is the measure of how likely something will occur.
  • It is the ratio of desired outcomes to total outcomes.
  • (# desired) / (# total)
  • Probabilities of all outcomes sums to 1.

• 2 - Example

• • If I roll a number cube, there are six total possibilities. (1,2,3,4,5,6)
  • Each possibility only has one outcome, so each has a PROBABILITY of 1/6.
  • For instance, the probability I roll a 2 is 1/6, since there is only a single 2 on the number cube.

• 3 - Practice

• • If I flip a coin, what is the probability I get heads?
  • What is the probability I get tails?
  • Remember, to think of how many possibilities there are.

• 4 - Answer

• • P(heads) = 1/2
  • P(tails) = 1/2
  • If you add these two up, you will get 1, which means the answers are probably right.

• 5 - Two or more events

• • If there are two or more events, you need to consider if it is happening at the same time or one after the other.

• 6 - “And”

• • If the two events are happening at the same time, you need to multiply the two probabilities together.
  • Usually, the questions use the word “and” when describing the outcomes.

• 7 - “Or”

• • If the two events are happening one after the other, you need to add the two probabilities.
  • Usually, the questions use the word “or” when describing the outcomes.

• 8 - Practice

• • If I roll a number cube and flip a coin:
  • What is the probability I will get a heads and a 6?
  • What is the probability I will get a tails or a 3?

• 9 - Answers

• • P(heads and 6) = 1/2 x 1/6 =1/12
  • P(tails or a 5) = 1/2 + 1/6 = 8/12 = 2/3

• 10- Experimental Probability

• • An experimental probability is one that happens as the result of an experiment.
  • (# of outcomes) / (# of trials)
  • The probabilities we have done so far are “theoretical probabilities”, because there was no experiment.

• 11- Experiment

• • Flip a coin 50 times, and write down what happens for each flip.
  • In the end, find the experimental probabilities by writing the how many times heads and tails occurred over the 
  • total number of trials (flips)
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-Fatehah & Balqis-