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Sal solves 32x3. Created by Sal Khan.
Video transcript
Let's try to calculate 3 times 32. And I'd like to rewrite it- this is one way of doing it- I like to rewrite it where I have the larger number on top so in this case it's 32 and I write the smaller number right below it and since the smaller number is only one digit- it's only a ones digit- I put that below the ones place on the larger number. So I'll put the 3 right over here and of course we can't forget our multiplication symbol and this is essentially a way of saying the same thing. You could read this as 32 times 3 But 32 times 3 is the exact same value as 3 times 32. It doesn't matter what order you multiply in. Now let's try to compute it. And once again this is only one way of doing it- there are many ways of doing it and I want you to think about why this works. So we can start we'll start with this 3 down here and we're going to multiply it by each of the digits in 32. We'll start with 3 times 2. Well, 3 times 2 from our multiplication tables- and you can figure out even if you didn't know your multiplication tables- is 6. 3 times 2- I'll write 6 right over here in the ones place. Now we're going to figure out what 3 times 3 is. Well once again we know that 3 times 3 is 9 and since I'm multiplying by the tens place right over here I'm going to put it in the tens place right like this. So we're done! We got 32 times 3 is 96. And I really encourage you to think about why this worked. And I'll give you a little bit of a hint here. I'll give you a little bit of a hint about why this worked. Remember 3 times 32 is the same thing as 3 times 30 plus 3 times 2. And if you look at it that way that's essentially what this process did. 3 times 2 is 6; 3 times 30 is 90. You add them up together you get 90 plus 6 is 96.