We now have the general

tools to really tackle any multiplication problems. So in this video I’m just going

to do a ton of examples. So let’s start off with–

and I’ll start in yellow. Let’s start off

with 32 times 18. Say 8 times 2 is 16. Well, I’ll do it in our head

this time because you always don’t have all this

space to work with. So 8 times 2 is 16. Put the 1 up there. 8 times 3 is 24. 24 plus 1 is 25. So 8 times 32 was 256. Now we’re going to have to

multiply this 1, which is really a 10, times 32. I’ll underline it

with the orange. 1 times 2– oh, we have

to be very careful here. 1 times 2 is 2. So you might say hey, let

me stick a 2 down there. Remember, this isn’t a 1. This is a 10, so we have

to stick a 0 there to remember that. So 10 times 2 is 20. Or you say 1 times 2 is 2, but

you’re putting it in the 2’s place, so you still get 20. So 10 times 2 is 20. It works out. Then 1 times 3. And we have to be very careful. Let’s get rid of what

we had from before. 1 times 3 is 3. There’s nothing to add

here, so you just get a 3. And so you get 10

times 32 is 320. This 1 right here, that’s a 10. 10 plus 8 is 18. So now we just add

up the two numbers. You add them up. 6 plus 0 is 6. 5 plus 2 is 7. 2 plus 3 is 5. Let’s keep going. Let’s do 99 times 88. So a big number. 8 times 9 is 72. Stick the 7 up there. And then you have

8 times 9 again. 8 times 9 is 72, but now

you have the 7 up here. So 72 plus 7 is 79. Fair enough. Now we’re done with this. Let’s just delete it just so

that we don’t get confused in our next step. In our next we’re going to

multiply this 8 now times 99. But this 8 is an 80. So let’s stick a 0 down there. 8 times 9 is 72. Stick a 7 up there. Then 8 times 9 is 72. Plus 7 is 79. 2 plus 0 is 2. Let me switch colors. 9 plus 2 is 11. Carry the 1. 1 plus 7 is 8. 8 plus 9 is 17. Carry the 1. 1 plus 7 is 8. 8,712. Let’s keep going. Can’t do enough of these. All right, 53 times 78. I think you’re getting

the hang of it now. Let’s multiply 8

times 53 first. So 8 times 3 is 24. Stick the 2 up there. 8 times 5 is 40. 40 plus 2 is 42. Now we’re going to have to

deal with that 7 right there, which is really a 70. So we got to remember

to put the 0 there. 7 times 3, and let’s

get rid of this. Don’t want to get confused. 7 times 3 is 21. Put the 1 there and

put the 2 up here. 7 times 5 is 35. Plus 2 is 37. Now we’re ready to add. 4 plus 0 is 4. 2 plus 1 is 3. 4 plus 7 is 11. Carry the 1. 1 plus 3 is 4. 4,134. Let’s up the stakes

a little bit. So let’s say I had

796 times 58. Let’s mix it up well. All right, so first we’re just

going to multiply 8 times 796. And notice, I’ve thrown in

an extra digit up here. So 8 times 6 is 48. Put the 4 up there. 8 times 9 is 72. Plus 4 is 76. And then 8 times 7 is 56. 56 plus 7 is 63. I’m sure I’ll make a

careless mistake at some point in this video. And the goal for you is to

identify if and when I do. All right, now we’re ready,

so we can get rid of these guys up here. Now we can multiply this 5,

which is in the 10’s place. It’s really a 50. Times this up here. Because it’s a 50 we

stick a 0 down there. 5 times 6 is 30. Put the 0 there, put

the 3 up there. 5 times 9 is 45. Plus the 3 is 48. 5 times 7 is 35. Plus 4 is 39. Now we’re ready to add. 8 plus 0 is 8. 6 plus 0 is 6. 3 plus 8 is 11. 1 plus 6 is 7. 7 plus 9 is 16. And then 1 plus 3 is 4. So 796 times 58 is 46,168. And that sounds about right

because 796– it’s almost 800. You know, which

is almost 1,000. So if we multiplied 1,000

times 58 we’d get 58,000. But we’re multiplying something

a little bit smaller than 1,000 times 58, so we’re getting

something a little bit smaller than 58,000. So the number is in

the correct ballpark. Now let’s do one more here

where I’m really going to step up the stakes. Let’s do 523 times– I’m going

to do a three-digit number now. Times 798. That’s a big

three-digit number. But it’s the same

exact process. And once you kind of see the

pattern you say, hey, this’ll apply to any number of digits

times any number of digits. It’ll just start taking you a

long time and your chances of making a careless mistake are

going to go up, but it’s the same idea. So we start with 8 times 523. 8 times 3 is 24. Stick the 2 up there. Now 8 times 2 is 16. 16 plus 2 is 18. Put the 1 up there. 8 times 5 is 40. Plus 1 is 41. So 8 times 523 is 4,184. We’re not done. We have to multiply times

the 90 and by the 700. So let’s do the 90 right there. So it’s a 90, so we’ll

stick a 0 there. It’s not a 9. And let’s get rid of

these guys right there. 9 times 3 is 27. 9 times 2 is 18. 18 plus 2 is 20. And then we have

9 times 5 is 45. 45 plus 2 is 47. I don’t want to

write that thick. 47. Let me make sure I did that

one right, and let’s just review it a little bit. 9 times 3 was 27. We wrote the 7 down here

and put the 2 up there. 9 times 2 is 18. We added 2 to that,

so we wrote 20. Wrote the 0 down there

and the 2 up there. The 9 times 5 was 45. Plus 2 is 47. You really have to make sure

you don’t make careless mistakes with these. Then finally, we have to

multiply the 7, which is really a 700 times 523. When it was just an 8 we just

started multiplying here. When it was a 90, when we

were dealing with the 10’s place, we put a 0 there. Now that we’re dealing with

something that’s in the 100’s, we’re going to

put two 0’s there. And so you have 7– and let’s

get rid of this stuff. That’ll just mess us up. 7 times 3 is 21. Put the 1 there. Stick the 2 up there. 7 times 2 is 14. 14 plus our 2 is 16. Put the 1 up there. 7 times 5 is 35. Plus 1 is 36. And now we’re ready to add. And hopefully we didn’t make

any careless mistakes. So 4 plus 0 plus 0. That’s easy. That’s 4. 8 plus 7 plus 0. That’s 15. Carry the 1. 1 plus 1 plus 1 is 3. 4 plus 7 plus 6. That’s what’s? 4 plus 6 is 10. It’s 17. And then we have 1 plus 4 is 5. 5 plus 6 is 11. Carry the 1. 1 plus 3 is 4. So 523 times 798 is 417,354. Now we can even

check to make sure. And so this is the

moment of truth. Let’s see if we

have– let’s see. 523 times 798. There you go. Moment of truth. I don’t have to

re-record this video. It’s 417,354. But we did it without the

calculator, which is the important point.

You helped me multiply. THANK YOU!!!

very easy

how was double digit multiplication invented and who invented it

Good job

Thank you!

😺✌🏾️

My family loves you guys! Thanks!!!! 😸👍🏽

i saw a mistake on 5:28 he shouldnt put 0 down he should put 3

Thanks

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I like Khan Academy. He teaches me many things and makes it understandable.

This helped my little brother

I will hate math forever

you helped me sooo much

Does anyone know what app or program he is using to do his presentation? Thanks.

Thank you for helping Khan!

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Khan acadamy do you know 1346556456592838 x 999999999999?

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I subbed!

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you made a mested up on the last one on the

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THANKS HELPED ALOT

I think that we should not put 0 we should put X

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you said and ut were not using decimals XD LOL

*WE

my teacher is always sayin "don't say and we are not using decimals"

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What about 378 x 9???

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Can some help me with math with digits

Thx!!!!

I have to watch this for homework then do 10 years of math

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when I first started khan academy I couldn't even subtract three digit numbers now I can multiply them!

This really helped me a lot! Thank you Khan Academy!

Did this intermediate and beginning of high school and then completely forgot about it smh

Esey

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