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### Course: 4th grade>Unit 8

Lesson 6: Adding and subtracting mixed numbers word problems

# 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.

## Want to join the conversation?

• is multiplication of fractions same as adding fractions
(16 votes)
• Also, when you multiply two fractions less than one, your answer actually gets smaller. Think about the multiplication sign as saying "groups of." 3 x 8 = 24 means 3 groups of 8 are 24.

With fractions, you're still saying that. 1/2 of a group of 12 is 6. 1/3 of a group of 9 is 3.

The procedure for two fractions is to multiply across -- numerator times numerator and denominator times denominator.

1/2 x 2/3 is saying that you have half of a group that was 2/3 of a full group to begin with. So, you had 2 thirds, but not you only have half of that, or 1/3

numerators : 1 x 2 = 2
denominators: 2 x 3 = 6

So the answer is 2/6, which can be reduced to the equivalent fraction 1/3.
(25 votes)
• so 3/4 of an hour is 45 min right?
(14 votes)
• yes an hour has 60 min so 1/4 of an hour is 15 min so multiply that by 3 and you get 45
(14 votes)
• Does the end result have to be a mixed fraction?
(8 votes)
• Not always. It could be a decimal for example.
(9 votes)
• how can you ad the tail and body together shouldent it be head body and tail?
(5 votes)
• wouldnt the fractions need to be changed to a mixed number
(2 votes)
• You COULD turn them into mixed numbers, but you don't NEED to. Often, fractions are easier to work with if they're improper fractions instead of mixed numbers.
(3 votes)
• A child's ladder is made of 3 sections each section is 3/4 meters long how long is the ladder when 3 sections are extended to make 1 ladder?
(2 votes)
• I received a quiz question which asked me to double 5/8. I assumed the answer would be 10/16. However, it was 5/8 x 2/1 = 10/8. Can someone please explain why 10/16 is incorrect and why 10/8 is correct?
(1 vote)
• 10/16 is incorrect and why 10/8 is correct John. When the question asked you to double, it means to multiply it by 2. When you multiply fractions, the bottom number doesn't change. So, you would multiply 5*2 and get 10. Then, add your denominator. Your correct answer is 10/8! I hope you understand.
(1 vote)
• why do you need to measure in fraction way, why not a another way?
(1 vote)
• Because it's useful. You could use decimals, but there are times when you cannot express as a decimal something like the irrational length.
(1 vote)
• why does he not count the tail but then adds the tail?
help
plzs
(1 vote)
• Sal does the body first to show how long it is, then he does the tail(To show how long it is) then he adds the amount of the tail and body(17/8- body + 10/8- tail = 27/8).
(1 vote)
• How do you change improper fraction into mixed number??
(1 vote)
• Divide. after all that's what the fraction bar means. Example:
17/6 is 2 remainder 5, so 2 is the whole number part, and the remainder is actually still in 6ths, so the answer is 2 5/6.
more examples
3/2 = 1 1/2
13/8 = 1 5/8
(1 vote)

## 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.