About this video
The video uses place value to compare 27 + 1 and 27 + 10. Adding 1 adds one more one, so the ones place goes from 7 to 8 and the answer is 28. Adding 10 adds one more ten, so the tens place goes from 2 to 3 and the answer is 37.
You'll be able to
- add 1 to a two-digit number by changing the ones place.
- add 10 to a two-digit number by changing the tens place.
- explain why adding 1 and adding 10 change different places.
Key words
- place value
- The value of a digit depends on where it is in the number.
- one's place
- The place on the right; it tells how many ones.
- ten's place
- The place to the left of the ones; it tells how many tens.
Transcript
- [Voiceover] So, pause this video and, real quick, figure out what 27 plus 1 is, and then, if possible, figure out what 27 plus 10 is. Alright, so, let's think about it together. So, you might've been able to do this one pretty easily. You might've said, "Okay! If I'm adding 1, "it's just going to be the next highest number from 27.
"I would go to 28 if I have 1 more." But, the reason why I'm doing this exercise is, we really think about place value. So, over here, the number 27, we have a 2 in the ten's place, this is in the ten's place, right over here, and then we have a 7 in the one's place.
So, you could visualize the number 27 as 2 tens, and I have 2 groups of 10 here, and then 7 ones, and I have 7 ones right over here. And then, if I add 1 more, that's 1 more of these individual ones, and so, what am I going to be left with? Well, I'm still going to have 2 tens, I'm still going to have 2 tens, but how many ones am I going to have now?
Oh, 1, 2, 3, 4, 5, 6, 7, 8 ones. So, it's going to be 28. So, that might not be surprising for you, but it's really valuable to think about in terms of place value because it can be very useful later on as you learn more math. Now, let's do the same thing with 27 plus 10.
We already said 27, that's 2 tens and 7 ones, and now, with 10, the 1 isn't in the one's place, so it doesn't just represent 1, the 1 here is in the ten's place, so we have 1 10 and we have 0 ones. So, we just have-- The number 10 is just a group of 10 here! So, when you add these together, what are you going to have?
Well, now, you're going to have 1, 2, 3 tens, you're going to have 3 in the ten's place, and you're still going to have 1, 2, 3, 4, 5, 6, 7 ones. 7 ones. So, notice. Here, when you added a 1, you increased your one's place by 1. And, here, when you added 10, which is really 1 10, you didn't increase the one's place, you increased the ten's place.
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