Dividing 2-digit numbers by 2-digit numbers
About this video
This video shows how to divide a 2-digit number by a 2-digit number using estimation and trial and error. It finds 92 ÷ 23 = 4 by thinking of 20 into 90, and 86 ÷ 15 = 5 remainder 11 by trying multiples of 15.
You'll be able to
- estimate a quotient by rounding the divisor and dividend.
- check a trial quotient by multiplying.
- find a remainder and explain why it must be less than the divisor.
Key words
- estimate
- A rough guess, like thinking of 23 as about 20, to help pick a number to try.
- remainder
- What is left over after dividing; it must be smaller than the number you divide by.
- trial and error
- Trying a number, checking it, and adjusting if it is too high or too low.
Transcript
- [Instructor] Let's get a little bit of practice dividing with two digit numbers. So let's start by trying to figure out what 92 divided by 23 is. Pause this video and see if you can figure that out. All right, now let's work through this together. So I am going to rewrite this.
We're gonna see how many times does 23 go into 92. So the first thing that I want to do, I just say, well, okay, 23 goes into 92. Let's think about it. 23 is roughly 20. 92 is roughly 90, so 20 times four would be 80, and that seems pretty close. 20 times five would be 100, so that goes over 90.
So I'm gonna try four here. Let's see if that works out. Four times three is 12, four times two is eight, plus one is nine. That worked out nicely. Four times 23 is exactly 92. I have no remainder, so there I have it. 92 divided by 23 is equal to four. Let's do another example.
Let's see if we can figure out what 86 divided by 15 is. Pause the video again and see if you can have a go at that. All right, so again, I will rewrite it. 15 goes into 86. All right, so here I'm going to have to estimate again, 86 is a little bit less than 90.
15 times two is 30, 15 times four is 60. 15 times six is 90, so that gets us too high. So it's going to be a little bit less than that, so let me just try 15 times five, or let me see if 15 goes into 86 five times. Five times five is 25. Five times one is five, of course, plus two is seven.
This is looking right, and then I have a remainder here. Six minus one is, sorry, six minus five is one, eight minus seven is one, and 11 is less than 15, so I can't divide into it anymore. And so this is five with a remainder 11. So the key when you're dividing by two digit numbers like this is try to estimate, and there is a little bit of an art to it.
You're going to have to say, okay, well, let me just try some number out. Maybe it's a little bit too low, maybe it's a little bit too high, and you're gonna have to do a little bit of trial and error, but that is okay. That is the way that everyone does it.
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