7.3 Probability
Probability is the likelihood that an event is going to happen.
Two events are independent events when one event doesn't affect the other event. Ex) tossing a coin and rolling a dice.
To figure out the probability of 2 independent events occurring, you have to look at the probability of each of the events separately.
Ex) What are the chances of tossing a coin with heads and rolling a 6.
Dice
Coin Toss
1
Heads
2
Tails
3 Probability=
Probability=
1
4
1
6
5
2
6
Now to look at the events together you have to look at all possible combinations.
1)You could roll a heads
2) You could roll a tails
Now how many possible combinations do you have?
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An easier way to calculate:
Keep the probability in fraction form for both events. Once you have the probability of each independent event, multiply the probabilities together.
Ex) coin toss prob= 1 dice roll prob= 1
2
6
Ex) What is the probability of spinning a 2 on the blue spinner and a 2 on the dice?
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Ex) A golf bag contains 9 white tees, 7 red tees and 4 blue tees. The golfer removes a tee from the bag, notes the color, then puts it back in her bag. The process is repeated. Find the probability of each event:
a) Both tees are red.
b) The first tee is not red and the second tee is blue.
*Think about how many tees you have.
Assignment pg. 411 #3­6, 8, 10, 12
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