Video: Using a Blank Number Line to Subtract within 1000

Scarlett is subtracting using a number line. Pick the calculation she is working on. What is the answer? [A] 733 − 482 [B] 733 − 428 [C] 733 − 284 [D] 733 − 248

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Video Transcript

Scarlett is subtracting using a number line. Pick the calculation she is working on. 733 subtract 482. 733 subtract 428. 733 subtract 284. 733 subtract 248. What is the answer?

We know that Scarlett is subtracting on a number line. This means Scarlett is counting back on a number line. Counting back is the same as subtracting. Scarlett starts with number 733. And all of our calculations begin at 733. So we’re starting counting at number 733.

First, Scarlett took away 200: 100, 200. So we know that our number has to have a two in the hundredth place because Scarlett took away 200. Both of these calculations have numbers which begin with 200. Next, Scarlett subtracts groups of 10: one, two, three, four. Scarlett took away four tens. Which of our numbers has four tens? It’s the last calculation. 248 has four tens. Finally, Scarlett took away three ones and then five more. Three and five more is eight. Does our number have eight ones? Yes, it does. The calculation that Scarlett is working on is 733 subtract 248. She took away two hundreds, four tens, and eight ones which is 248.

Now, we need to calculate the answer to this subtraction — 733 subtract 248. Let’s start in the ones column. We need to take eight away from three. We need some more ones. Three is less than eight. So we can take a ten from the tens column and add it to our ones. Now we have two tens. Now we can work out 13 take away eight which is five. But we don’t have enough tens in the tens place. We have two and we need to take away four. So we can take a hundred and add 10 tens to our two in the tens column. Now we have 12 tens. 12 take away four leaves us with eight. Now we can subtract in the hundredth column. Six take away two is four. 733 take away 248 equals 485.

The calculation Scarlett is working on is 733 take away 248. And the answer is 485.

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