Early math review
Sal subtracts 3-digit numbers by subtracting ones, tens, and hundreds.
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- at0:38is the word hundred a number and place value?(6 votes)
- Should I use I calculator if I think I can do it in my head?(2 votes)
- It's useful to be able to perform arithmetic (addition, subtraction, etc.) in your head, and you'll get faster at it than using a calculator! If you're unsure of the value you come up with, you can always use a calculator to check your result.(7 votes)
- If 300-200=100, what is 200-300?(4 votes)
- If you have for example, 400 - 150 = 250, then if you switch it around, so that it is 150 - 400, it will always be -250.
So 300 - 200 = 100, switch it around (200 - 300) and we get -100 instead of 100.
Im sorry if this is confusing but it's a neat trick that can really come in handy.(3 votes)
- [Voiceover] Let's think about how many blocks we have here. What number these blocks represent. Well, I have four groups of a hundred here, so I could say that I have four hundreds. Four hundreds. I have three groups of 10 here. So I could write plus three tens. Plus three tens. And then I have six ones here. So I could write plus six ones. Plus six ones. And, so I can write that as... I could write that as... I could write a six in the ones place for my six ones. Three in the tens place for my three tens. For my three tens. And then a four in the hundreds place for my four hundreds. So this is 436. Four hundred thirty-six. 436. Now let's subtract from that. Let's subtract from that... Let's subtract from that the number... the number 300... 312. 312 and let's think about what we would do here for subtracting 300... If we are subtracting 312. Well, we had six ones before, we're taking away two ones. So let me write that down. We're gonna take away two ones. We're taking away one 10. So we're taking away one 10. So minus one 10. And we're taking away three hundreds. So we're taking away... So we're taking away three hundreds. Three hundreds. So what's that going to do to us? What's that going to do to us? Well, we had four hundreds, we're taking away three hundreds, so let's take them away. Let's take away... Let's take away the... Let's take way the one... two... and three hundreds and we're just left with one hundred. One hundred. We could do it over here. Four hundreds minus three hundreds is going to be one hundred. Now we had three tens, we're taking away one ten. So let's do that. So we're going to be left with two tens. So plus two tens. Three minus one is two. Three minus one is two. And then last, then we had six ones, we're taking away two ones, and we're going to be left with four ones. Six minus two is four. Six minus two is four. And we're done! 436 minus 312 is 124. And you see how we did that. We took away three hundreds. We took away one ten. And we took away two ones. To get 124. Which is one hundred, two tens, and four ones.