It is defined as the difference between the upper-class limit and the lower class limit. Class Interval = Upper-Class limit – Lower class limit.
What is an approximate interval?
- If you know the exact distribution of the test statistic, and use that distribution's quantiles to make confidence intervals, that interval is exact. If you approximate the distribution of the test statistic, then the interval is approximate.
- The Empirical rule states that for a normal distribution, nearly all of the data will fall within three standard deviations of the mean . The empirical rule is further illustrated below
- The Empirical Rule states that, for a normally distributed random variable:
- 68% of the measures are within 1 standard deviation of the mean.
- 95% of the measures are within 2 standard deviation of the mean.
- 99.7% of the measures are within 3 standard deviations of the mean.
In this problem, we have that:
- 68% of data falls within the first standard deviation from the mean.
- 95% fall within two standard deviations.
- 99.7% fall within three standard deviations.
- From the information given, the mean is $150 and the standard deviation is $20.
2 standard deviations = 2 × 20 = 40
150 - 40 = $110
150 + 40 = 190
Therefore, about 95% of the monthly food expenditures are between $110 and $190
Mean = 150
Standard deviation = 20
- 95% of the monthly food expenditures are between what two amounts:
- By the Empirical Rule, within 2 standard deviations of the mean
150 - 2*20 = $110
150 + 2*20 = $190
$110 and $190
To learn more about observations refer to:
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