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## Staging content lifeboat

### Course: Staging content lifeboat>Unit 14

Lesson 36: Multiplying fractions

# Multiplying 2 fractions: number line

Learn the concept of multiplying fractions by fractions. Watch as the process is visually represented on a number line, helping to understand the 'why' behind the procedure.  Created by Sal Khan.

## Want to join the conversation?

• At , doesn't Sal mean the two halves?
• He's dividing the halves into fourths
• Why does he make this more confuseing than it needs to be?
• Then look at other video! He is trying his best!
• 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.
• I do not understand this. Could you make more simpimler? Please?
• he is trying to
• Why did you use a number line when you could do 2/3 x 4/5 which is easier then number line ?
Why do it the hardier way which is slower, when you could go the easier way which is way faster? You still get the write answer anyway so why not do it the faster way?
• It's just to prove the concept that you are going 2/3 to 4/5 or 4/5 to 2/3, you can't just get that from looking at "2/3 x 4/5", you wouldn't know how you got the product from those numbers, yes you did multiplicate the fractions but why do you do that when they are not whole numbers?
• is there a different way to do this ?
• Yes, there is. I actually answered a question just like this a couple of minutes ago... :D The way Mr. Khan likes to do it is by explaining it in a way that teaches you the concept so you understand what you're doing. But the simpler way is actually, well.... a lot simpler. For example, if you're multiplying 1/8 by 2/5, first you multiply the numerators by each other (1 x 2) to get an answer of 2. Then you multiply the denominators by each other (8 x 5) to get 40. Finally, you put the 2 as your numerator and the 40 as your denominator to get a product of 2/40, but that isn't your final answer because each number can be simplified -- each divided by 2 -- to get a final product of 1/20. I hope this helped you!
• umm i don't understand how it become 1/8 2/8 3/8 in number line ?
• On the number line, there is an increase (increment) of 1/8 each time. Each time a 1/8 is added, there will be that increase (e.g. after adding 1/8 to 0, the result is 1/8; after adding a 1/8 to the already present 1/8, the result is 2/8; adding another 1/8 to the 2 one-eighths gives a 3/8; adding yet another 1/8 to the 3 one-eighths gives a 4/8, etc.)