Based on historical weather data in a certain city, about 62% of the days are cloudy. Find the mean, standard deviation, and variance for the number of cloudy days in a 30-day month.
Table of contents
- 1. Introduction to Statistics53m
- 2. Describing Data with Tables and Graphs2h 1m
- 3. Describing Data Numerically1h 48m
- 4. Probability2h 26m
- 5. Binomial Distribution & Discrete Random Variables2h 55m
- 6. Normal Distribution & Continuous Random Variables1h 48m
- 7. Sampling Distributions & Confidence Intervals: Mean2h 8m
- 8. Sampling Distributions & Confidence Intervals: Proportion1h 20m
- 9. Hypothesis Testing for One Sample2h 23m
- 10. Hypothesis Testing for Two Samples3h 25m
- 11. Correlation1h 6m
- 12. Regression1h 4m
- 13. Chi-Square Tests & Goodness of Fit1h 30m
- 14. ANOVA1h 4m
5. Binomial Distribution & Discrete Random Variables
Binomial Distribution
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A biologist is monitoring a large bird sanctuary where a particular bird species is known to have a 70% success rate for each nesting attempt (at least one chick fledges from the nest). This season, she observes 500 independent nesting attempts across the sanctuary.
(C) What is the probability that at least 330 nesting attempts are successful?
A
0.02
B
0.005
C
0.98
D
0.03

1
Step 1: Recognize that this is a binomial probability problem. The number of trials (n) is 500, the probability of success (p) for each trial is 0.7, and we are interested in the probability of at least 330 successes.
Step 2: To simplify the calculation, approximate the binomial distribution using a normal distribution. The mean (μ) and standard deviation (σ) of the binomial distribution can be calculated as follows: μ = n * p and σ = sqrt(n * p * (1 - p)).
Step 3: Convert the problem to a normal distribution problem. Use the continuity correction by adjusting the value of 330 to 329.5 (since we are looking for 'at least 330').
Step 4: Standardize the value 329.5 to a z-score using the formula: z = (X - μ) / σ, where X is the value of interest (329.5), μ is the mean, and σ is the standard deviation.
Step 5: Use the standard normal distribution table or a statistical software to find the probability corresponding to the calculated z-score. Subtract this probability from 1 to find the probability of at least 330 successes.
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