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Early math review
Course: Early math review > Unit 5
Lesson 5: Intro to subtraction with 2-digit numbersSubtracting 2-digit numbers without regrouping 1
Sal subtracts 23 from 65 by thinking about tens and ones.
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What is a column?(9 votes)
a column is just a vertical area, so all the elements in the column are stacked on top of each other.
you can see in the video that the ones "column" is just the vertical area that he dotted around and all the elements inside that column (the 5 ones, the 3 ones and the 2 ones) are put each one on top of the other.(8 votes)
- When you "carry" digits what is that referring to(3 votes)
Hi Lynel. A carry is a digit that is transferred from one column of digits to another column of more significant digits. For ex. when 6 and 7 are added to make 13, the "3" is written to the same column and the "1" is carried to the left.(4 votes)
I have a question. When you have a zero, and you need to borrow from it, you cross it off, and put a nine, right? But, what if you need to subtract zero from another number that is higher than zero, like 5? Do you cross off the nine and put an eight? :o(3 votes)
No, you do not put a nine. You put a ten. Then you subtract the numbers.
Your second question is asking what is 5 minus 0. In this case, since zero is at the bottom, you can take away nothing from five. The answer is five. But if it is 0 minus 5, you will be going in the negative side of the number line. This would mean that 0 minus 5 is -5. Draw the number line. Start at zero. Minus means to the left. Plus means to the right.
If you have a five in the ones place and a nine on the bottom (i.e. 765 minus 39), then the five becomes into a 15 and the 6 becomes into a 5.
Think about it like this: if you are decreasing the 6, you are removing ten from the number, which is going to change the problem, which you do not want. So, to compensate for that "lost" ten, you add it to the five, and make it into a fifteen, so you can remove 9, since you cannot remove 9 from 5 (in this case since the first number in its entirety is larger than the second number).
Hope this helps:)(3 votes)
Is there a reason why the numbers are stacked on top of each other for problems like this? Like, why do you put the 65 above the 23?(1 vote)
Well, one: to line up the places so no mistakes would be made. And two: to make it easier for regrouping. My 4th grade teacher called this old-fashioned math and I guessed I kinda liked it. But 65 and 23, I just do it in my head because they're pretty simple equations. But if I was working with decimal places or multiplication or addition with four 3-digit numbers, I would stack them up.(3 votes)
Can you add in any situation in subtraction?(1 vote)- Yes, such as :
3-(-3)
=3+3
=6(3 votes)
Video transcript
- [Voiceover] Let's try now to subtract some two-digit numbers. Over here, we have 65 minus 23, and I encourage you to pause the video and see if you could figure this out. I'm assuming you've had a try at it. Let's do it together. The way I like to do it is
I start in the ones place, and the numbers in the ones place I've colored them in in yellow, so this right over here is the ones place. This over here in purple
is the tens place. I could even do a column here, where everything in yellow,
this is the ones column. I guess you could think of it that way, everything there is in the ones place. They're representing a
certain number of ones, and then everything in the second column, everything in the second
column is in the tens place. They represent a certain number, a certain number of tens. 65 is six 10s and five ones. 23 is two 10s and three ones. One way to do it is, say, let's look at the ones place first. I'm taking three ones away from five ones. Five ones minus three ones is two ones. Then, you can go to the tens place. Six 10s minus two 10s, well,
that's going to be four 10s, four 10s, and there you have it. This is equal to 42, and once again, I could have written it multiple ways. I could have written it like this. I could have written 65 as 6 tens, six tens, + 5 ones, plus 5 ones. I didn't write over here
because when I have something in this place, that means it's tens, but here I can write it out, 6 tens. If I'm subtracting 23, that's the same thing
as subtracting two 10s, subtracting 2 tens, and then subtracting three ones, and then subtracting 3 ones, subtracting 3 ones. What's that going to be? Well, 5 ones - 3 ones is
exactly what we have over here. It's going to be 2 ones, and 6 tens - 2 tens, well, that's just going
to be 4 tens, 4 tens. 6 tens + 5 ones - 2 tens - 3 ones is going to be 4 tens and 2 ones, four 10s and two ones, or 42. 42 is equal to 4 tens + 2 ones. Hopefully, that makes
a little bit of sense.