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When only grouped data are available, how is the midpoint of each class interval found?
ADivide the class frequency by the class width
BTake the lower boundary of the class interval
CAdd the two boundaries and divide the sum by two
DSubtract the lower boundary from the upper one
Answer & Solution
Correct answer: C. Add the two boundaries and divide the sum by two
1. Grouped data hide the individual values, so each class is represented by one figure.
2. That figure is the midpoint, formed by adding the lower and upper boundaries and halving the sum.
3. Each midpoint is then weighted by its class frequency to estimate the mean.
4. Subtracting the boundaries gives the class width, which sets the size of the interval rather than its centre.
_Source: OpenStax Introductory Business Statistics (CC BY 4.0), Ch 2 "Descriptive Statistics", section 2.3 Measures of the Center of the Data_
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