Grade point averages of students on a large campus follow a...

Grade point averages of students on a large campus follow a normal distribution with a mean of 2.6 and a standard deviation of 0.5 . a. One student is chosen at random from this campus. What is the probability that this student has a grade point average higher than 3.0 ? b. One student is chosen at random from this campus. What is the probability that this student has a grade point average between 2.25 and 2.75 ? c. What is the minimum grade point average needed for a student's grade point average to be among the highest $10 \%$ on this campus? d. A random sample of 400 students is chosen from this campus. What is the probability that at least 80 of these students have grade point averages higher than 3.0 ? e. Two students are chosen at random from this campus. What is the probability that at least one of them has a grade point average higher than 3.0 ?

Grade point averages of students on a large campus follow a normal distribution with a mean of 2.6 and a standard deviation of 0.5 .
a. One student is chosen at random from this campus. What is the probability that this student has a grade point average higher than 3.0 ?
b. One student is chosen at random from this campus. What is the probability that this student has a grade point average between 2.25 and 2.75 ?
c. What is the minimum grade point average needed for a student's grade point average to be among the highest $10 \%$ on this campus?
d. A random sample of 400 students is chosen from this campus. What is the probability that at least 80 of these students have grade point averages higher than 3.0 ?
e. Two students are chosen at random from this campus. What is the probability that at least one of them has a grade point average higher than 3.0 ?

Key Concepts

Complement Rule in Probability

The complement rule states that the probability of an event occurring is equal to one minus the probability of it not occurring. This rule is useful for calculating 'at least one' probabilities by first finding the probability of the event not happening at all and subtracting it from one.

Normal Approximation to the Binomial Distribution

For a large number of trials, the binomial distribution can be approximated using the normal distribution, provided certain conditions are met. This approximation simplifies calculations by allowing the use of continuous probability techniques for discrete outcomes.

Binomial Distribution

The binomial distribution describes the probability of a fixed number of successes in a series of independent trials, each with the same probability of success. It is applicable when dealing with discrete events that follow a yes/no outcome pattern.

Percentile and Quantile Calculations

Percentiles and quantiles are values that divide the data into intervals based on cumulative probability. In the context of normal distributions, finding a particular percentile (e.g., the top 10%) involves using the inverse cumulative distribution function to determine the corresponding threshold value.

Normal Distribution

The normal distribution is a continuous, symmetric probability distribution characterized by its mean and standard deviation. It is widely used in statistics to model real-world phenomena where data tend to cluster around the mean, forming a bell-shaped curve.

Z-Score (Standardization)

A z-score indicates how many standard deviations an observation is from the mean. By converting a value to its corresponding z-score, any normal distribution problem can be standardized to the standard normal distribution, making it easier to compute probabilities.

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