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## 2nd grade

### Course: 2nd grade > Unit 4

Lesson 1: Visually adding within 1,000# Adding and subtracting on number line

Sal adds and subtracts numbers like 585 and 368 using a number line. Numbers used in these problems are less than 1000.

## Want to join the conversation?

- im kinda confused so basicley just adding numbers but seperatly and on a number line?(16 votes)
- Yes, that is exactly correct. The point of the exercise is being able to see and understand how breaking down larger number such as 264 + 354. On a number line, we could start with 264 then depict the addition of 300 + 50 + 4. It helps you visualize the response.(18 votes)

- This is so hard! i still don't undersand(8 votes)
- Adding and subtracting on number lines is just another way of showing how to add and subtract. For example, if the question was 2 plus 2, the arrow would first go to 2, then to 4, the answer.

Or if the question wass 110+255, the arrows may first go to 100, then 110, then 310, then 360, then 365 using place value, adding 100 + 10 + 200 + 50 + 5.(6 votes)

- Why do we do this? I am asking this because I know this(4 votes)
- We are doing this because we are struggling and it builds our brains stronger(12 votes)

- dude im 8 not 2th im in 3rd(8 votes)
- exactly who asked?(3 votes)

- ohhh i get it i see ok(6 votes)
- it was a good way to teach kids(6 votes)
- ho can I solve this problem make it better undersdtanding(5 votes)
- You can use your fingers to get to your answer(2 votes)

- khan academy become famous(5 votes)
- how do i get the question corte(4 votes)
- How should I know.(1 vote)

## Video transcript

- Which number line shows 361 + 544? Let's see, in all of them we're starting at 361, so now let's add 544. This one starts with adding 400, and then 50, and then 4, it's adding 454, not 544. Now this one adds 500, then 40, and then 4, so this is adding 544, to 361, we see that it is 905. This makes sense, you add 500, you get 861, you add 40, you get to 901, and then add the 4, you get 905, so definitely go with that choice. This one over here, instead of add 500, you add 50, which doesn't make sense because we're clearly adding 5 hundreds, 4 tens, or 40, and then 4 ones, let's do some more examples. Which expression can be solved with the following number line? Let's see, we're starting at 718, and then we're adding 200, and then we're adding 40 to get to 958. This is really 718 + 240, which is this choice right over there. This is kind of, strangely fun. Which number line shows 585 - 368? Let's see, these second two number lines, both start at 585, we're starting our computation at 585, this one's starting at 558, so it swapped the numbers, so this one doesn't make sense, but let's look at these two choices. We want to subtract 3 hundreds, 6 tens, and 8 ones. In both of these, we subtract 3 hundreds, and then we want to subtract 6 tens, 6 tens, and then 8 ones, that's this one over here. This one swaps the... instead of having 6 tens and 8 ones, it has 8 tens and 6 ones, so it swapped... this is subtracting 386, which isn't the original problem, so definitely like this third choice. Let's do one more example. Which expression has been solved with the following number line? We're starting at 935, and then we're going to subtract 400, and then we're going to subtract 20. This is 935 - 420. 935 - 420, that choice right over there.