- Add and subtract within 100: FAQ
- Adding 2-digit numbers without regrouping
- Understanding place value when adding ones
- Understanding place value when adding tens
- Adding with regrouping
- Add within 100 using place value blocks
- Addition and subtraction with number lines
- Add within 100 using a number line
Sal adds 23 + 30 by thinking about place value.
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- How would you draw 100 or 1000 cubes?(80 votes)
- You define another symbol for 10, 100, 1000 cubes or any other grouping that can be multiplied by a manageable amount. Otherwise, with a lot of patience and perseverence :)(40 votes)
- How is it important to put the biggest number on top?(8 votes)
- I guess this depends on the scenario (not defined) and if you are better at addition vs. subtraction (in an equation requiring one of those functions. Maybe not so much the biggest number vs. testing the position and the mechanics you use to get there and comparing it to a different method to see what worked quicker. Then again, you could do something that you are weak at to gain strength as well.
If you want a better answer without the 'coaching', define a specific scenario where you saw this to help someone answer it in context.(14 votes)
- 23 is the same as 2 tens and 3 ones why not 2 ones and 3 tens?(4 votes)
- That would be 32. The 2 is in the tens place and 3 is in the ones place so that is 23 if 3 is the tens place and 2 is in the ones place it would be back wards. You would not get the right answer.Just the basics that would answer your question on why you cannot switch the placesa(7 votes)
- [Voiceover] So in the number 23, we have a two in the 10's place. So, that two literally represents two 10s. And we see it right over here. We have two groups of 10 blocks. This is a 10 and this is a 10. So this two literally represents two 10s. One 10 and two 10s. Now this three is in the one's place, and it represents three ones. We can see them right over here. One, two, three blocks. And of course, if you had three ones together with two 10s. These two 10s, represent 20, and these three ones represent three, so you get 23. So, let's write that down. So we can write down the 23. 23 is equal to two 10s, two 10s plus three ones, plus three, three ones. Now what would happen if I added 20 to 23. Let me do that, so let's say... Actually let me do something more interesting. Let's say we take 23, and to that we add 30. So, let's add, let's add 30. Three zero, three zero. So, what is this going to be? Well, I start with 23, which I have represented here, and I'm going to add 30. 30 has a three in the 10's place, so it literally means I'm going to add three 10s and I'm going to add zero ones. So, let me add those three 10s. So, that's one 10... this is two 10s... and then that is three 10s. So I've added one, two and three 10s here. So now, now, how many 10s do I have? Well, I now have one, two, three, four, five 10s. Now notice, two 10s plus three 10s is equal to five 10s. So now I have five 10s. And how many ones do I have? Well, I still have those three ones, and you can think of it this way, three ones plus zero ones is still going to be three ones. Three ones. So, what's 23, what's 23 plus 30 going to be? Let me rewrite it, 23 plus 30, is going to be equal to, well, five 10s, we can just write that as a five in the 10's place, represents five 10s, or 50, and then we're going to have three ones. Whoops, let me do that in a different, in the ones color, in that orange color. Is the three ones. So, 23 plus 30 is 53. You have two 10s plus three 10s, give you five 10s, three ones plus zero ones is equal to three ones.