Mathematics
Grade 8
15 min
Probability of opposite, mutually exclusive, and overlapping events
Probability of opposite, mutually exclusive, and overlapping events
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1
Introduction & Learning Objectives
Learning Objectives
Define and identify opposite (complementary) events.
Calculate the probability of an opposite event occurring.
Distinguish between mutually exclusive and overlapping events.
Apply the correct formula to calculate the probability of mutually exclusive events.
Apply the correct formula to calculate the probability of overlapping events.
Solve real-world problems involving opposite, mutually exclusive, and overlapping probabilities.
Have you ever wondered about the chances of something *not* happening, or the likelihood of one thing *or* another occurring? 🤔 Probability helps us understand these possibilities!
In this lesson, we'll explore different types of events and how to calculate their probabilities. You'll learn about events that can'...
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Key Concepts & Vocabulary
TermDefinitionExample
ProbabilityThe measure of how likely an event is to occur, expressed as a number between 0 and 1 (or 0% and 100%).The probability of flipping a coin and getting heads is 1/2 or 50%.
EventA specific outcome or a set of outcomes from an experiment or situation.Rolling a '4' on a standard six-sided die is an event.
Opposite Event (Complement)The event that an original event does *not* occur. If 'A' is an event, its opposite is denoted as A' (read as 'A prime' or 'not A').If event A is 'rolling an even number', then A' (the opposite event) is 'rolling an odd number'.
Mutually Exclusive EventsTwo events that cannot happen at the same time. If one event occurs, the other cannot.When rolling a single die,...
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Core Formulas
Probability of an Opposite Event
$P(A') = 1 - P(A)$
To find the probability that an event A does *not* happen, subtract the probability of A happening from 1 (or 100%). This is useful when it's easier to calculate the probability of the event happening than not happening.
Probability of Mutually Exclusive Events (OR Rule)
$P(A \text{ or } B) = P(A) + P(B)$
If two events, A and B, cannot occur at the same time (they are mutually exclusive), the probability that either A *or* B occurs is the sum of their individual probabilities.
Probability of Overlapping Events (OR Rule)
$P(A \text{ or } B) = P(A) + P(B) - P(A \text{ and } B)$
If two events, A and B, *can* occur at the same time (they are overlapping), the probability that either A *or* B occurs is the sum...
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Challenging
Two standard six-sided dice are rolled. What is the probability that the sum of the numbers is 4 OR that both dice show the same number (a 'double')?
A.9/36
B.10/36
C.3/36
D.8/36
Challenging
If you are told that for two events A and B, the probability P(A or B) is exactly equal to P(A) + P(B), what can you conclude about the relationship between A and B?
A.Events A and B must be mutually exclusive.
B.Events A and B must be overlapping.
C.Event B must be the opposite of event A.
D.Events A and B must be certain events.
Challenging
A survey of 200 Grade 8 students at a camp found that 120 students can swim, 80 can canoe, and 50 students can do neither. What is the probability that a randomly selected student can swim OR canoe?
A.200/200
B.150/200
C.150/200
D.50/200
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