Staging content lifeboat
Course: Staging content lifeboat > Unit 14Lesson 15: Adding and subtracting fractions: 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.
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- is multiplication of fractions same as adding fractions(10 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.(13 votes)
- so 3/4 of an hour is 45 min right?(9 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(9 votes)
- The lizard is very nice.(10 votes)
- Does the end result have to be a mixed fraction?(6 votes)
- Not always. It could be a decimal for example.(5 votes)
- um did sal draw the lizard (sorry if this was against the rules im just curious!) ?(7 votes)
- I kind of get confused with the ruler thingy but it is very helpful, in fact I get it now just by looking at the problem so... nah.(7 votes)
- ok its good that u understand it now so....yeah!(1 vote)
- how can you ad the tail and body together shouldent it be head body and tail?(4 votes)
- how did u draw it so good on computer man?(4 votes)
- you are teaching me so much it's just been hard in 5th grade.(4 votes)
- i got confused on the last one(3 votes)
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.