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Multiplying 3-digit by 2-digit numbers | Grade 5 (TX TEKS) | Khan Academy

2m read
·Nov 10, 2024

Let's get a little bit of practice multiplying numbers. So, what is 365 times 84? I encourage you to pause this video; hopefully, you have some scratch paper around, and try to calculate what this is.

All right, now let's do this together. What I like to do is, let me first write 365, and then let me write 84 right under that. But make sure that I line up the place values. So I put the eight in the tens place right under that six, and the four in the ones place right under that five.

Now I am ready to multiply. The first thing I'm going to do is I'm going to multiply 365 by 4. So, 4 times 5 is 20; I'll put the zero in the ones place, and I'll regroup that two because it's really 2 tens. So, 4 times 6 is 24 plus that two; we're really talking about 24 tens. So, plus another two tens is going to be 26 tens. I'll put six tens right over here, and then I'll regroup the two up here.

Now I have 4 times 3; it's really 4 times 300. But 4 times 3 is 12 plus those two that I just regrouped is 14. So, let me put the 14 hundreds here. Now, let me worry about this eight. Well, this eight is in the tens place; it's really 80. So, let me just put a zero here.

I start in the tens place, and let me get rid of these characters right over here so I don't confuse myself. So, 8 times 5 is 40; I'll put the zero right over here and regroup the four. 8 times 6 is 48, and then I add that four; it's going to get me to 52. Then, 8 times 3 is 24 plus 5 is going to be 29.

Now I can add everything together: 0 plus 0 is 0; 6 plus 0 is 6; 4 plus 2 is 6; 1 plus 9 is 10; put the zero here and regroup the one. 1 plus 2 is 3, and I'm done. I got 3,660.

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