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Fraction word problem: lizard

Sal solves a fraction word problem about the length of a lizard.  The fractions have common denominators.  Created by Sal Khan.

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Video transcript

James and Karlee caught a lizard in their backyard. Its body is 17/8 inches long, and its tail is 10/8 inches long. What is the length of the lizard's body and tail together? So good thing we have the lizard obediently standing next to our measuring stick or our ruler or whatever this happens to be. And we have it marked off in inches. And not only that, we have it marked off in eighths of inches. Notice-- this is an inch, and we have 1, 2, 3, 4, 5, 6, 7, 8 sections of that actual inch. So, let's see, 17/8 inches long. This is going to be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17. This right over here is 17/8, which you might notice is also equal to 2 and 1/8. 8 goes into 17 two times with a remainder of 1. But we won't talk about that just yet. But we see that's the length of the lizard's body-- 17/8. I just counted off 17 of these 8's right over here-- 17/8. And then they say that the tail is 10/8 inches long. So it's another 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. So this distance right over here, I just counted off 10/8. So that's another 10/8 inches long, and it gets us all the way to the end of the lizard's tail. And they say what is the length of the lizard's body and tail together? Well, that's going to be the length of the body plus the length of the tail. So you have 17/8 plus 10/8. Well, that's going to get you to 17 plus 10/8, which is equal to 27-- 27/8. And so this mark right over here is 27/8. And if you wanted to write this as a mixed number, you could just say, well, 8 goes into 27 three times, and you have a remainder of 3. So this is equal to 3 and 3/8. And you see that on the ruler right over here. It's equal to 1, 2, 3. And then we have another 1, 2, 3/8. These two things are equivalent.