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The average winter daily temperature in Chicago has a distribution that is approximately Normal, with a mean of 28 degrees and a standard deviation of 8 degrees. What percentage of winter days in Chicago have a daily temperature of 35 degrees or warmer? (Source: wunderground.com)

Short Answer

Expert verified
Approximately 19.1% of winter days in Chicago have a daily temperature of 35 degrees or warmer.

Step by step solution

01

Standardize the Temperature Value

First, convert the temperature value of 35 to a z-score. The z-score is a measure of how many standard deviations an element is from the mean. It can be calculated using the formula \( z = \frac{X - μ}{σ} \), where X is the data point, μ is the mean and σ is the standard deviation. In this case, X is 35 (the temperature we are interested in), μ is 28 (the average temperature) and σ is 8 (the standard deviation). This gives \( z = \frac{35 - 28}{8} \) which simplifies to \( z ≈ 0.875 \).
02

Calculate the Area to the Right of the Z-Score

Now we need to calculate the percentage of data that lies to the right of the calculated z-score. This requires checking a standard normal distribution table or using software or a calculator with statistical capabilities. To find this value, we look for the z-score in the table which gives us the area to the left of the z-score. But we need the area to the right which is \( 1 - (Area to the left) \). If you look up the area to the left of 0.875 from the table, it will be about 0.809. We subtract this from 1 to get the area to the right. This leaves \( 1 - 0.809 = 0.191 \).
03

Convert Fraction to Percentage

The last step is to convert this decimal to a percentage, as the question asks for a percentage. Multiplying by 100, we get \( 0.191 * 100 = 19.1\% \).

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