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Normal Distributions & z-Scores · Easy Worksheet 2

Normal Distributions & z-Scores — Easy Worksheet 2

Grade 11 · MathSheets    Name: ____________________   Date: __________

Use z = (x - μ) / σ and the 68-95-99.7 rule.

How to solve

A z-score, z = (x - μ) ÷ σ, tells how many standard deviations a value is from the mean. In a normal distribution about 68% of the data is within 1 standard deviation of the mean, 95% within 2 and 99.7% within 3. On each side of the mean that gives bands of 34%, 13.5%, 2.35% and 0.15%.

Example

The test scores are normally distributed with mean 75 and standard deviation 6. Find the z-score of 87.

Answer: 2

right so far
1. The test scores are normally distributed with mean 75 and standard deviation 6. Find the z-score of 81.
2. About what percent of the data lies in the shaded region? (Use the 68-95-99.7 rule.)
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3. The commute times in minutes are normally distributed with mean 30 and standard deviation 4. Which value has a z-score of 2.5?
4. The battery lifetimes in hours are normally distributed with mean 40 and standard deviation 5. About what percent of the data is above 30?
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5. About what percent of the data lies in the shaded region? (Use the 68-95-99.7 rule.)
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6. The battery lifetimes in hours are normally distributed with mean 40 and standard deviation 5. Find the z-score of 50.
7. The cereal box weights in grams are normally distributed with mean 500 and standard deviation 10. About what percent of the data is above 520?
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8. About what percent of the data lies in the shaded region? (Use the 68-95-99.7 rule.)
470480490500510520530

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