Mathematics
Grade 12
15 min
Independence and conditional probability
Independence and conditional probability
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1
Introduction & Learning Objectives
Learning Objectives
Define conditional probability and independence in the context of a variable parameter 'n'.
Set up probability expressions as functions of a variable 'n' that represents a growing population or number of trials.
Calculate the limit of a conditional probability P(A|B) as n approaches infinity.
Use limits to determine if two events become independent as the number of trials or population size approaches infinity (asymptotic independence).
Apply the rules for limits of rational functions to solve complex probability problems.
Interpret the meaning of a limiting probability of 0, 1, or a value in between in the context of a real-world scenario.
What's the real chance of picking a specific person out of a crowd if the crowd size grows...
2
Key Concepts & Vocabulary
TermDefinitionExample
Conditional ProbabilityThe probability of an event (A) occurring, given that another event (B) has already occurred. It is denoted by P(A|B).In a deck of 52 cards, the probability of drawing a King, given that you've already drawn a Queen (and not replaced it), is P(King|Queen) = 4/51.
Independence of EventsTwo events are independent if the occurrence of one does not affect the probability of the other occurring. Mathematically, P(A and B) = P(A) * P(B).Flipping a coin twice. The outcome of the first flip (Heads) does not affect the probability of the second flip being Heads. P(Heads on 1st and Heads on 2nd) = (1/2) * (1/2) = 1/4.
Limit at InfinityThe value that a function f(n) approaches as the variable 'n' increases or decreases without bound. It des...
3
Core Formulas
Conditional Probability Formula
P(A|B) = \frac{P(A \cap B)}{P(B)}
Use this formula to find the probability of event A happening, on the condition that event B has already happened. P(A ∩ B) is the probability that both A and B occur.
Test for Independence
P(A \cap B) = P(A) \cdot P(B)
Two events A and B are independent if and only if the probability of them both occurring is equal to the product of their individual probabilities. An equivalent test is P(A|B) = P(A).
Limit of a Rational Function at Infinity
\lim_{n \to \infty} \frac{a_k n^k + \dots}{b_m n^m + \dots} = \begin{cases} 0 & k < m \\ \frac{a_k}{b_m} & k = m \\ \pm\infty & k > m \end{cases}
To find the limit of a ratio of polynomials as n -> infinity, compare the degrees of the numerator...
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Easy
Two events A_n and B_n, whose probabilities depend on a parameter 'n', are considered asymptotically independent if which of the following conditions is true?
A.P(A_n | B_n) = P(A_n) for all values of n > 0.
B.lim_{n→∞} P(A_n | B_n) = lim_{n→∞} P(A_n)
C.lim_{n→∞} P(A_n ∩ B_n) = 0
D.The events are mutually exclusive for a sufficiently large n.
Easy
A bag contains 5 red marbles and 'n' blue marbles. A single marble is drawn at random. What is the limit of the probability of drawing a red marble as n approaches infinity?
A.1
B.1/5
C.0
D.5
Easy
Which formula correctly defines the conditional probability of event A occurring, given that event B has already occurred?
A.P(A|B) = P(A) ⋅ P(B)
B.P(A|B) = P(A ∩ B) / P(A)
C.P(A|B) = P(B) / P(A ∩ B)
D.P(A|B) = P(A ∩ B) / P(B)
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