Adding 3-digit and 1-digit numbers together

Watch: Adding one-digit and three-digit numbers

When you add a 1-digit number to a 3-digit number, the same rules apply as when you are adding a 1-digit number to a 1 or 2-digit number.

Number lines, partitioning, Base 10 and the column method can all be useful.

Learn more about adding a 1-digit to a 3-digit number in this video.

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What is 285 + 6?

Let's solve this with a number line. Start on the number 285 and then count on 6.

Notice how both digits in the tens and ones have changed? That’s because you bridged a ten when six was added.

285 + 6 = 291

Another good way to solve the question is to partition the number 6:

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Now that 6 has been partitioned into 5 and 1, you can use your number bond knowledge to add the 5 to reach the next ten, then add 1.

First add the 5 to take you to the next ten (290).

285 + 5 = 290

Then add the 1.

290 + 1 = 291

What is 422 + 4?

Let's use Base 10 this time:

How would you add a 3-digit number and a 1-digit number using the column method?

What is 239 + 4?

Let's try using the column method to solve this question.

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Lay the question out like this, with the 4 underneath the 9 in the ones column.
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Start in the ones column. 9 + 4 = 13. You would write the 3 in 13 in the ones column and then carry over the ten. This is to make sure each digit still has the right place value.
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Now move to the tens column. 3 tens + 1 ten = 4 tens.
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Finally move to the hundreds column. There is only two-hundred with nothing to add to it. So 200 add nothing is 200. You have the answer: 239 + 4 = 243.