Interpreting line plots

We're told that the weights of 11 different babies are recorded in the line plot below, and we see there's one, two, three, four, five, six, seven, eight, nine, ten, eleven data points; each one represents a different baby whose weight is recorded. Each weight was rounded to the nearest one-eighth of a pound.

All right, then they ask us what is the difference in weight between the two heaviest babies. So, pause this video and try to figure that out before we work through it together.

All right, now where are the two heaviest babies? So this one out here, this is the heaviest baby. And what is its weight? Let's see, its weight is right over there. And what is that number or what is that weight? So this is 9, and this is 10, and we have one, two, three, four, five, six, seven, eight equal spaces. So each of these is an eighth.

So this is nine and one, two, nine and two-eighths. So this one is—let me write this—this is nine and two-eighths. Another way to think about it is two-eighths is the same thing as one-fourth because if you think about it as one, two, three, four equal spaces, this is also nine and one-fourth of the way to ten. So this is the same thing as nine and one-fourth.

And then what's the second-heaviest baby? Because we want the weight difference between the two heaviest. So the second heaviest baby is right over here, and we know that it is eight and a half pounds.

So what we really need to do is figure out what is the difference between nine and two-eighths, or nine and one-fourth, and eight and a half, right over here? So we could set this up as a subtraction. This is going to be nine—and let's call it nine and one-fourth—minus eight and a half.

We can actually use these measurement scales or you can even do this as something of a number line to help us think about this. The difference is this length right over here, and we could think about it in terms of eighths because each of these hash marks is an eighth. So one-eighth, two-eighths, three-eighths, four-eighths, five-eighths, and six-eighths.

So this is equal to six-eighths. We could also think about it in terms of fourths, so this is one-fourth, two-fourths, and three-fourths. So this is equal to three-fourths.

So what's the difference in weight between the two heaviest babies? It is three-fourths of a pound.