Identifying the class width in a histogram

Intro

Howdy!  I'm Professor Curtis of Aspire Mountain Academy here with more statistics homework help.  Today we're going to learn how to identify the class width in a histogram.  Here's our problem statement: The histogram to the right represents the weights in pounds of members of a certain high school programming team.  What is the class width?  What are the approximate lower and upper class limits of the first class?

Part 1: Calculate the class width

OK, so here's our data.  We have the option here to blow it up bigger if we want, but we don't really need to do that; we can see what we need to see right here.  So the class width — notice that for each of these bins (which are each of the bars that you see here), you have lower class limits listed here at the bottom of your graph.  So 110 is the lower class limit for this first bin, 130 is the lower class limit for the second bin, 150 is the lower class limit for this third bin, so on and so forth.

So the class width is just going to be the difference between successive lower class limits.  Or we could use upper class limits, but it's easier to use lower class limits because they're right here on the graph.  And it doesn't matter which two you use as long as the one that comes right after the other.

So let's just use the first two bins lower class limits 130 and 110.  So if I take 130, subtract 110, that gives me the difference, which is the class width (20).  I put that here in my answer field, and check my answer.  Good job!

Part 2: Find the lower and upper class limits

Next, what are the approximate lower and upper class limits of the first class?  Well, the first class is this first bin here.  We can see 110 listed here; that's the lower class limit.  So we'll stick that there in our answer field.  And in the other answer field, we need the upper class limit.  That's going to be just barely to the next lower class limit but not quite there.  And the way we get that is by taking that lower class limit and just subtracting 1 from final digit place.

So here we have whole numbers; 130 is a whole number.  So we're gonna subtract 1 from 130 to get 129; that's our approximate upper class limit.  Check the answer.  Excellent!

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