Introduction
- Probability is a branch of mathematics that deals with the likelihood of events occurring.
- It plays a significant role in various fields such as statistics, gambling, and finance.
- In this lecture, we will learn about the basic concepts of probability.
Terminologies
- Experiment: Any activity or process that leads to an outcome is called an experiment.
- Outcome: The result of an experiment is called an outcome.
- Sample Space: The set of all possible outcomes of an experiment is called the sample space.
- Event: Any subset of the sample space is called an event.
Types of Probability
- Theoretical Probability: is the likelihood of an event occurring based on mathematical reasoning.
- Experimental Probability: is the likelihood of an event occurring based on conducting experiments or trials.
Probability Calculation
- Probability is expressed as a number between 0 and 1, where 0 represents impossibility and 1 represents certainty.
- The probability of an event A is denoted as P(A).
- Classical Probability Formula: P(A) = (Number of favorable outcomes) / (Total number of possible outcomes)
- Relative Frequency Probability Formula: P(A) = (Number of times event A occurred) / (Total number of trials or experiments)
- Complementary Probability Formula: P(A’) = 1 - P(A)
Independent and Dependent Events
- Independent Events: When the outcome of one event does not affect the outcome of another event, they are called independent events.
- Dependent Events: When the outcome of one event affects the outcome of another event, they are called dependent events.
Addition Rule of Probability
- General Addition Rule: P(A or B) = P(A) + P(B) - P(A and B)
Multiplication Rule of Probability
- General Multiplication Rule: P(A and B) = P(A) * P(B|A)
Permutations
- Permutations are arrangements of objects in a specific order.
- The nPermuteR formula is used to calculate permutations: nPr = n! / (n - r)!
Combinations
- Combinations are arrangements of objects where the order does not matter.
- The nChooseR formula is used to calculate combinations: nCr = n! / [(n - r)! * r!]
Conditional Probability
- Conditional probability is the probability of an event occurring given that another event has already occurred.
- The formula for conditional probability is: P(A|B) = P(A and B) / P(B)
Bayes’ Theorem
- Bayes’ Theorem is used to calculate the probability of an event happening based on prior knowledge.
- The formula for Bayes’ Theorem is: P(A|B) = [P(B|A) * P(A)] / P(B)
Probability Distributions
- A probability distribution is a mathematical function that describes the likelihood of various outcomes in an experiment.
- Examples of probability distributions include the binomial distribution, normal distribution, and Poisson distribution.
Random Variables
- A random variable is a variable that takes on different values depending on the outcome of an experiment.
- Random variables can be classified as discrete or continuous.
Expected Value
- The expected value, also known as the mean or average, represents the long-term average outcome of a random variable.
- It is calculated by multiplying each possible outcome by its probability and summing them up.
Variance and Standard Deviation
- Variance measures the spread or dispersion of a random variable’s values.
- Standard deviation is the square root of the variance and provides a measure of the average deviation from the mean.
Normal Distribution
- The normal distribution is a continuous probability distribution that is symmetric and bell-shaped.
- It is widely used in statistical analysis and is often referred to as the Gaussian distribution.
Central Limit Theorem
- The Central Limit Theorem states that the sampling distribution of the sample mean approaches a normal distribution as the sample size increases.
Hypothesis Testing
- Hypothesis testing is a statistical method used to make inferences or draw conclusions about a population based on sample data.
- It involves formulating null and alternative hypotheses and testing them using statistical tests.
Probability - Problem 5- Question
- A bag contains 5 red balls and 3 green balls.
- Two balls are drawn from the bag without replacement.
- What is the probability that both balls are green?
Probability - Problem 5- Solution
- Step 1: Determine the total number of balls in the bag: 8 (5 red + 3 green)
- Step 2: Determine the number of ways to choose 2 green balls from 3:
- Combination formula: nCr = n! / [(n - r)! * r!]
- n = 3 (number of green balls), r = 2 (number of balls drawn)
- nCr = 3! / [(3 - 2)! * 2!] = 3
- Step 3: Determine the number of ways to choose any 2 balls from 8:
- Combination formula: nCr = n! / [(n - r)! * r!]
- n = 8 (total number of balls), r = 2 (number of balls drawn)
- nCr = 8! / [(8 - 2)! * 2!] = 28
- Step 4: Calculate the probability: P(2 green balls) = (number of ways to choose 2 green balls) / (number of ways to choose any 2 balls)
- P(2 green balls) = 3 / 28 = 0.107
Probability - Problem 6- Question
- A fair die is rolled 3 times.
- What is the probability that the sum of the numbers obtained is 15?
Probability - Problem 6- Solution
- Step 1: Determine the total number of outcomes when a die is rolled 3 times: 6^3 = 216
- Step 2: Find the number of favorable outcomes where the sum of the numbers is 15:
- Possible combinations: (4,5,6), (5,4,6), (5,5,5), (5,6,4), (6,4,5), (6,5,4), (6,6,3)
- Total number of favorable outcomes: 7
- Step 3: Calculate the probability: P(sum of numbers = 15) = (number of favorable outcomes) / (total number of outcomes)
- P(sum of numbers = 15) = 7 / 216 ≈ 0.0324
Probability - Problem 7- Question
- A bag contains 5 red balls, 3 green balls, and 2 blue balls.
- Three balls are drawn from the bag without replacement.
- What is the probability that exactly 2 balls are red?
Probability - Problem 7- Solution
- Step 1: Determine the total number of balls in the bag: 10 (5 red + 3 green + 2 blue)
- Step 2: Determine the number of ways to choose exactly 2 red balls:
- Combination formula: nCr = n! / [(n - r)! * r!]
- n = 5 (number of red balls), r = 2 (number of red balls drawn)
- nCr = 5! / [(5 - 2)! * 2!] = 10
- Step 3: Determine the number of ways to choose any 3 balls from 10:
- Combination formula: nCr = n! / [(n - r)! * r!]
- n = 10 (total number of balls), r = 3 (number of balls drawn)
- nCr = 10! / [(10 - 3)! * 3!] = 120
- Step 4: Calculate the probability: P(2 red balls) = (number of ways to choose 2 red balls) / (number of ways to choose any 3 balls)
- P(2 red balls) = 10 / 120 = 0.0833
Probability - Problem 8- Question
- In a box, there are 5 red balls, 3 green balls, and 2 blue balls.
- Two balls are chosen at random from the box with replacement.
- What is the probability that both balls are red?
Probability - Problem 8- Solution
- Step 1: Determine the total number of balls in the box: 10 (5 red + 3 green + 2 blue)
- Step 2: Calculate the probability of drawing a red ball: P(red ball) = (number of red balls) / (total number of balls)
- P(red ball) = 5 / 10 = 0.5
- Step 3: Calculate the probability of drawing two red balls with replacement = P(red ball) * P(red ball)
- P(both balls are red) = 0.5 * 0.5 = 0.25
Probability - Problem 9- Question
- A box contains 2 red balls and 3 green balls.
- Four balls are drawn from the box without replacement.
- What is the probability that all four balls are green?
Probability - Problem 9- Solution
- Step 1: Determine the total number of balls in the box: 5 (2 red + 3 green)
- Step 2: Determine the number of ways to choose all four green balls:
- Combination formula: nCr = n! / [(n - r)! * r!]
- n = 3 (number of green balls), r = 4 (number of balls drawn)
- nCr = 3! / [(3 - 4)! * 4!] = 0 (as it is not possible to choose 4 green balls from 3)
- Step 3: Calculate the probability: P(all four balls are green) = (number of ways to choose all four green balls) / (total number of ways to choose any four balls)
- P(all four balls are green) = 0 / (5! / [(5 - 4)! * 4!]) = 0
Probability - Problem 10- Question
- A deck of cards contains 52 cards, including 4 aces.
- Two cards are drawn from the deck without replacement.
- What is the probability that both cards are aces?
Probability - Problem 10- Solution
- Step 1: Determine the total number of cards in the deck: 52
- Step 2: Determine the number of ways to choose 2 aces from 4:
- Combination formula: nCr = n! / [(n - r)! * r!]
- n = 4 (number of aces), r = 2 (number of cards drawn)
- nCr = 4! / [(4 - 2)! * 2!] = 6
- Step 3: Determine the number of ways to choose any 2 cards from 52:
- Combination formula: nCr = n! / [(n - r)! * r!]
- n = 52 (total number of cards), r = 2 (number of cards drawn)
- nCr = 52! / [(52 - 2)! * 2!] = 1326
- Step 4: Calculate the probability: P(both cards are aces) = (number of ways to choose 2 aces) / (number of ways to choose any 2 cards)
- P(both cards are aces) = 6 / 1326 ≈ 0.0045
Probability - Problem 11- Question
- A bag contains 8 red balls and 4 green balls.
- Two balls are drawn from the bag, one by one, without replacement.
- What is the probability that the first ball is red and the second ball is green?
Probability - Problem 11- Solution
- Step 1: Determine the total number of balls in the bag: 12 (8 red + 4 green)
- Step 2: Calculate the probability of drawing a red ball on the first draw: P(red ball) = (number of red balls) / (total number of balls)
- P(red ball) = 8 / 12 = 0.6667
- Step 3: Calculate the probability of drawing a green ball on the second draw, given that the first ball was red: P(green ball | first ball is red) = (number of green balls) / (total number of balls - 1)
- P(green ball | first ball is red) = 4 / 11 ≈ 0.3636
- Step 4: Calculate the probability of the first ball being red and the second ball being green: P(first ball is red and second ball is green) = P(red ball) * P(green ball | first ball is red)
- P(first ball is red and second ball is green) = 0.6667 * 0.3636 ≈ 0.2424
Probability - Problem 12- Question
- A jar contains 6 red balls and 4 blue balls.
- Three balls are drawn from the jar without replacement.
- What is the probability that at least two balls are blue?
Probability - Problem 12- Solution
- Step 1: Determine the total number of balls in the jar: 10 (6 red + 4 blue)
- Step 2: Determine the number of ways to choose all three blue balls:
- Combination formula: nCr = n! / [(n - r)! * r!]
- n = 4 (number of blue balls), r = 3 (number of balls drawn)
- nCr = 4! / [(4 - 3)! * 3!] = 4
- Step 3: Determine the number of ways to choose exactly two blue balls:
- Combination formula: nCr = n! / [(n - r)! * r!]
- n = 4 (number of blue balls), r = 2 (number of balls drawn)
- nCr = 4! / [(4 - 2)! * 2!] = 6
- Step 4: Determine the number of ways to choose any three balls:
- Combination formula: nCr = n! / [(n - r)! * r!]
- n = 10 (total number of balls), r = 3 (number of balls drawn)
- nCr = 10! / [(10 - 3)! * 3!] = 120
- Step 5: Calculate the probability: P(at least two balls are blue) = (number of ways to choose all three blue balls + number of ways to choose exactly two blue balls) / (number of ways to choose any three balls)
- P(at least two balls are blue) = (4 + 6) / 120 = 0.0833
Probability - Problem 13- Question
- A box contains 5 red balls and 7 green balls.
- Three balls are drawn from the box without replacement.
- What is the probability that all three balls are the same color?
Probability - Problem 13- Solution
- Step 1: Determine the total number of balls in the box: 12 (5 red + 7 green)
- Step 2: Determine the number of ways to choose all three red balls:
- Combination formula: nCr = n! / [(n - r)! * r!]
- n = 5 (number of red balls), r = 3 (number of balls drawn)
- nCr = 5! / [(5 - 3)! * 3!] = 10
- Step 3: Determine the number of ways to choose all three green balls:
- Combination formula: nCr = n! / [(n - r)! * r!]
- n = 7 (number of green balls), r = 3 (number of balls drawn)
- nCr = 7! / [(7 - 3)! * 3!] = 35
- Step 4: Determine the number of ways to choose any three balls:
- Combination formula: nCr = n! / [(n - r)! * r!]
- n = 12 (total number of balls), r = 3 (number of balls drawn)
- nCr = 12! / [(12 - 3)! * 3!] = 220
- Step 5: Calculate the probability: P(all three balls are the same color) = (number of ways to choose all three red balls + number of ways to choose all three green balls) / (number of ways to choose any three balls)
- P(all three balls are the same color) = (10 + 35) / 220 = 0.25
Probability - Problem 14- Question
- A bag contains 4 green balls, 3 red balls, and 5 blue balls.
- Three balls are drawn from the bag without replacement.
- What is the probability that the first ball is blue, the second ball is red, and the third ball is green?
Probability - Problem 14- Solution
- Step 1: Determine the total number of balls in the bag: 12 (4 green + 3 red + 5 blue)
- Step 2: Calculate the probability of drawing a blue ball on the first draw: P(blue ball) = (number of blue balls) / (total number of balls)
- P(blue ball) = 5 / 12 ≈ 0.4167
- Step 3: Calculate the probability of drawing a red ball on the second draw, given that the first ball was blue: P(red ball | first ball is blue) = (number of red balls) / (total number of balls - 1)
- P(red ball | first ball is blue) = 3 / 11 ≈ 0.