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# Multiplying 2 fractions: number line

Sal uses a number line to multiply fractions. Created by Sal Khan.

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• At , doesn't Sal mean the two halves? • Why does he make this more confuseing than it needs to be? • I do not understand this. Could you make more simpimler? Please? • The Number Line approach is interesting but its hard to do unless you have a notebook and pencil with you but in the case where you have to quickly solve a question like "If the tax refund (lets say 1200\$) is being divided between 4 people, how large of a fraction is each person getting?", and you don't happen to have a pencil and notebook by your side, how could you more easily do a question like that in your head? • If you're dividing 1 whole among 4 people, then each person gets 1/4 of whatever it is you're dividing.

Something tells me that's not what you meant, though. Because 1200 is a nice multiple of 100, we can simply drop the zeroes and add them back later on. The problem then changes from 1200/4 to 12/4. 12/4 can be simplified to 3 (4 + 4 + 4 = 12), and then tack the zeroes back on - we get a result of \$300.
• umm i don't understand how it become 1/8 2/8 3/8 in number line ? • When i'm adding fractions do I need to add the numerator • • • In some cases, yes! It might be really easy to use division for this sort of thing, when you have a nice whole number, (like 6) and a nice and clean, simple fraction, (like 1/2) and you know that 1/2 of 6 is the same as dividing 6 by 2. However, with numbers that are impossible to apply this method to, (like 13/89 of 24.12) multiplication must be used instead. I hope that answers your question. :)

Edit: With the numbers I gave ( 13/89 of 24.12) , the problem might also look something like this: 13/89 -Divided by- 1/24.12 Because any number (x) multiplied by and other number (y) is the same as dividing x by the reciprocal of y.
In this case, It's not "impossible" to find the answer this way like I said before, but multiplying would be far easier to dividing by the reciprocal, Hope that helps. :)
• I know that the person is trying their best but, i still don't understand the number line. Could somebody help me understand it? or could somebody put it by part so i could understand it a little bit better? • If you multiply or divide the top and bottom of any fraction by the same number, you do not change the value of the fraction. If you modify only top or only bottom you are changing the value of the fraction.
Here are examples.
Let's say I have a fraction of 1/2. That's half.
I can multiply top and bottom by 2. (1*2)/(2*2) = 2/4. Now I made 2 quarters. Guess what? 2 quarters is one half. 1/2=2/4. These two fractions look different, but they represent the same value.

Take a pizza, divide it into 12 equal slices, take 3 slices. How much pizza did you get? 3/12. I can divide top and bottom by 3. (3/3)/(12/3) = 1/4. Take a look at the 3 slices you got. You have a quarter of a pizza. So 3/12 = 1/4

In the video the fraction was (5 * 2) / (6 * 3). We can divide top and bottom by 2 and the value will not change. (5 * 2 / 2) / (6 * 3 / 2). 2 / 2 = 1 and 6 / 2 = 3. You'll get (5 * 1) / (3 * 3). That is what you've seen in the video.
Let's compare (5 * 2) / (6 * 3) = 10/18. Divide top and bottom by 2 you'll get 5/9. (5 * 1) / (3 * 3) = 5/9. The same!! If you take 2 pizzas and divide one into 18 equal slices and then take 10 slices, the other divide into 9 slices and take 5 of them, you'll get the same amount of pizza.
Let's take original fraction (5 * 2) / (6 * 3) and try to divide only the bottom part (5 * 2) / (6 / 3 * 3 / 3) = (5 * 2) / (3 * 1) = 10/3 That is totally different value. That fraction means 3 whole pizzas and one third of fourth pizza. This does not equal to our original fraction.
Lengthy explanation, but I hope it is helpful. 