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# Addition, subtraction, and estimation: FAQ

## What is the difference between rounding and estimating?

Rounding is one way of estimating. When we round, we adjust a number to the nearest "round" number (like the nearest ten, hundred, or thousand). Estimating can also involve guessing or using other strategies to come up with an approximate answer.
Here are a couple of the exercises that practice rounding:

## What is multi-digit addition?

Multi-digit addition is just like regular addition, except that the numbers we're adding have more than one digit. The key is to line the numbers up so that the place values match. For example, to add $265$ and $348$, we would write:
$\overline{)\begin{array}{rl}& 265\\ +& 348\end{array}}$
Starting on the right side, we add $5$ (from the ones place) and $8$ (from the ones place) to get $13$. We write the $3$ down and carry the $1$ (from the tens place) over to the next column.
Next, we add $6$ (from the tens place) and $4$ (from the tens place) to get $10$. We add the $1$ that we carried over to get $11$. We write the $1$ down and carry the $1$ (from the hundreds place) over to the next column.
Finally, we add $2$ (from the hundreds place) and $3$ (from the hundreds place) to get $5$. We add the $1$ that we carried over to get $6$.
So the sum of $265$ and $348$ is $613$.
Practice with our exercise Multi-digit addition.

## What is multi-digit subtraction?

Multi-digit subtraction is similar to multi-digit addition, except that we're taking one number away from another. Again, the key is to line the numbers up so that the place values match. For example, to subtract $278$ from $437$, we would write:
$\overline{)\begin{array}{rl}& 437\\ -& 278\end{array}}$
Starting on the right side, we subtract $8$ (from the ones place) from $7$ (from the ones place). Since we don't have enough ones in the ones place, we need to regroup from the tens place. We can take one ten from the tens place, which leaves us with $2$ in the tens place. We add that ten to the $7$ in the ones place, which gives us $17$. Now we can subtract $8$ from $17$ to get $9$.
Next, we subtract $7$ (from the tens place) from $2$ (from the tens place). Again, we need to regroup from the next place value. We take one hundred from the hundreds place, which leaves us with $3$ in the hundreds place. We add that hundred to the $2$ in the tens place, which gives us $120$. Now we can subtract $70$ from $120$ to get $50$.
Finally, we subtract $2$ (from the hundreds place) from $3$ (from the hundreds place) to get $1$.
So the difference between $437$ and $278$ is $159$
Practice with our exercise Multi-digit subtraction.

## When do we use these skills in the real world?

We use these skills all the time! We might round numbers when we're estimating the cost of items at the store, or when we're trying to get a rough idea of how much time a project will take. We use multi-digit addition and subtraction when we're working with larger numbers, like when we're balancing our bank account or measuring distances.

## Want to join the conversation?

• what will happen if we have an adding and subtraction problem at the same time what would we have to do in order to solve the question?
• Good question,

It does matter, because (10 - 5) - 2 isn't the same as 10 - (5 - 2). But what if we have addition and subtraction? According to PEMDAS rule which states the order of operations addition and subtraction happens "at the same time", but as we know that isn't helpful, because sometimes the answer of a question depends on it's order of calculations. Personally, I and many others that study this field some way or other, we do addition and subtraction left to right.

So if we have a question like:

12 - 6 + 5 =

I will first calculate 12 - 6 and then + 5

6 + 5 =
11

Hope that helps.
• Please give me some more um thoose things where you divede like this 169 dived by 0 = 168
• 169/0 is undefined, not 168.
One way to see why is because no number, when multiplied by 0, can ever get you 169.
• thanks
• I watched the video at on how to round thousands but I am still confused a whole lot. How do I round thousands?
• say it's round thousand's and you have 18,364 if the thousand's are 5 or a larger number than you turn it from 18,364 to 20,000
• if were trying to solve the equation shown, we would have to borrow the tens to make it possible to subtract 8 from 7.
• what would happen if i had a lot of digits like this

98
34
68
67
74
38
82
+ __

what if you do not know the answer because you don't know the number.
• That would be weird
• what does multiply mean