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Hi Azariel,

When determining class width follow this simple guideline. If the class width calculation gives you a decimal round to the nearest whole number. If the class width turns out to be a whole number, try using the next highest whole number. 

Usually, the value will need to be higher than the calculation of width = range/# of classes. Remember that formula only provides the smallest width that might work. It typically does not work. The only way to know for sure is to try to form your classes with the value to see if the last class contains your largest data value. If it does, you have an acceptable width (note: there is more than one correct answer for these problems).

See the video below for more detail,

Professor McGuckian