# Example of 1-Sample Z

A scientist for a company that manufactures processed food wants to assess the percentage of fat in the company's bottled sauce. The advertised percentage is 15%. The scientist measures the percentage of fat in 20 random samples. Previous measurements found that the population standard deviation is 2.6%.

The scientist performs a 1-sample Z-test to determine whether the fat percentage differs from 15%.

1. Open the sample data, FatContent.MTW.
2. Open the 1-Sample Z dialog box.
• Mac: Statistics > 1-Sample Inference > Z
• PC: STATISTICS > One Sample > Z
3. From the drop-down list, select Sample data in a column.
4. In Sample, enter Percent Fat.
5. In Known standard deviation, enter 2.6.
6. Select Perform hypothesis test.
7. In Hypothesized mean, enter 15.
8. Click OK.

## Interpret the results

The null hypothesis states that the mean of the percentage of fat equals 15%. Because the p-value is 0.012, which is less than the significance level of 0.05, the scientist rejects the null hypothesis. The results indicate that mean percentage of fat differs from 15%.

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