Multiplying 3-digit by 2-digit numbers
About this video
The video multiplies 365 x 84 with the standard algorithm. It lines up place values, finds 365 x 4 = 1,460, puts a zero placeholder for the 8 (really 80) to find 365 x 80 = 29,200, then adds the rows to get 30,660.
You'll be able to
- line up place values to multiply a 3-digit number by a 2-digit number.
- regroup correctly while multiplying.
- use a placeholder zero when multiplying by the tens digit.
Key words
- place value
- What a digit is worth because of its position, like the 8 in 84 meaning 80.
- regroup
- Move extra tens or hundreds to the next place, like carrying the 2 from 20.
- placeholder zero
- A 0 written in the ones place when multiplying by a tens digit.
Transcript
- [Instructor] Let's get a little bit of practice multiplying numbers. So what is 365 times 84? So I encourage you, pause this video, hopefully you have some scratch paper around and try to calculate what this is. Alright, now let's do this together. So what I like to do, 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. And now I am ready to multiply. So the first thing I'm gonna do, is I'm gonna multiply the 365 times four.
So four times five is 20. I'll put the zero in the ones place and I'll regroup that two 'cause it's really two tens. So four times six 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.
And now I have four times three. It's really four times 300, but four times three is 12, plus those two that I just regrouped is 14. So let me put the 14 hundreds here. And now let me worry about this eight. Well, this eight is in the tens place, it's really eighty.
So let me just put a zero here. So I start in the tens place and let me get rid of these characters right over here, so I don't confuse myself. So eight times five is 40. I'll put the zero right over here, regroup the four, eight times six is 48. And then I add that four, it's going to get me to 52.
52. And then eight times three is 24, plus five is going to be 29. And now I can add everything together. Zero plus zero is zero, six plus zero is six, four plus two is six, one plus nine is 10. Put the zero here, regroup the one, one plus two is three. And I'm done. I got 30,660.
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