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The birthday problem What's the probability that in a randomly selected group of 30 unrelated people, at least two have the same birthday? Let's make two assumptions to simplify the problem. First, we'll ignore the possibility of a February 29 birthday. Second, we assume that a randomly chosen person is equally likely to be born on each of the remaining 365 days of the year. (a) How would you use random digits to imitate one repetition of the process? What variable would you measure? (b) Use technology to perform 5 repetitions. Record the outcome of each repetition. (c) Would you be surprised to learn that the theoretical probability is 0.71 ? Why or why not?

Short Answer

Expert verified
Simulate birthdays with random numbers, repeat 5 times to check matches. 0.71 probability is not surprising if shared birthdays found.

Step by step solution

01

Understanding the Birthday Problem

The problem states that we want to find the probability that in a group of 30 people, at least two share the same birthday. We'll use assumptions where each person is equally likely to be born on any day over 365 days, ignoring February 29.
02

Part (a): Simulating the Process Using Random Digits

To simulate one repetition of this process using random digits, assign each digit (or set of digits) to represent a day of the year, such as values from 1 to 365. Choose 30 random sets of digits to represent the birthdays. Record if any two numbers repeat (indicating shared birthdays). The variable measured is whether at least one pair of people has the same birthday.
03

Part (b): Performing 5 Repetitions Using Technology

Use a random number generator to simulate 365 days, selecting 30 day-numbers for each repetition. Repeat the process 5 times, noting each outcome where at least two numbers are equal (indicating shared birthdays). Record results as either 'yes' (shared birthdays found) or 'no' for each repetition.
04

Part (c): Evaluating Theoretical Probability Outcome

Theoretical calculations for the probability of at least two people in a group of 30 sharing the same birthday is approximately 0.71. Given five trials, a range of outcomes is possible. If the majority of trials show shared birthdays, this aligns well with the theory, suggesting 0.71 is plausible, not surprising.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

birthday problem
The birthday problem is a fascinating concept in probability theory. It explores the likelihood that within a group of people, some will share the same birthday. At first glance, it may seem rare for birthdays to coincide, but probability tells a different story when the number of people reaches a certain size.
Usually, the surprising result is that even with only 23 people in a room, there's already a more than 50% chance that two people share a birthday. The exercise increases this group to 30 people, boosting the chance significantly. This counterintuitive solution stems from the vast number of possible pairs that can be formed from the group.
The assumed conditions in the exercise help simplify the calculations. By ignoring leap day (February 29) and assuming each birthday is equally probable, the problem becomes more manageable. This hypothetical simplification allows us to focus solely on the probability aspect without getting bogged down by irrelevant real-world complications.
random digits
In statistics and probability exercises, random digits are a valuable tool for simulating random events. When solving the birthday problem, we can mimic the distribution of birthdays by using random digits between 1 and 365. Each number represents a potential birthday for a person in our group.
For example, you can use a table of random digits or a calculator to generate 30 random numbers, each corresponding to one day of the year. If any of these numbers appear more than once in the set, it indicates that at least two people share the same birthday.
Random digits are an essential component in simulations, as they allow us to model real-world processes in a straightforward and repeatable way. They help us understand complex probability problems, giving us insights that can otherwise feel unclear.
random number generator
A random number generator (RNG) is a computational tool designed to produce a sequence of numbers that lack any pattern, essentially mimicking the process of random selection. When applied to the birthday problem, an RNG can efficiently simulate the birthdate assignment for a group of 30 people.
Given the assumptions of equal birthday distribution over the 365 days, a random number generator selects numbers within this range. By repeating this multiple times, we can perform trials that reveal how often shared birthdays occur. This process provides a concrete method to estimate probability through empirical data.
Technological advancements have made RNGs widely accessible, allowing students and researchers to explore probabilistic concepts with ease. By utilizing this technology, we gain practical insight into the randomness of different scenarios, reinforcing our theoretical understanding.
theoretical probability
Theoretical probability is an approach that calculates the likelihood of an event based on the possible outcomes, rather than experimental or simulated data. For the birthday problem, this involves determining mathematically the chance of at least two people sharing a birthday in a group.
The mathematically derived probability that at least two people out of 30 share the same birthday is approximately 0.71, or 71%. This calculation considers all the ways in which birthdays can overlap, providing a powerful insight that challenges our intuitive expectations.
Understanding theoretical probability helps in gauging how likely an event is without needing to physically perform trials. It serves as a benchmark, allowing us to compare theoretical results with those obtained from simulations and experiments, facilitating a deeper comprehension of probability concepts.

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Most popular questions from this chapter

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