Double-Digit Addition: The Complete Mission

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What is Step 1 when adding two-digit numbers, like $47 + 35$?

Step 1: Add the digits in the ones column. $7 + 5 = 12$.

You're adding $47 + 35$. After adding the ones to get $12$, what is Step 2?

Step 2: Regroup. Write the $2$ in the ones place of the answer and carry the $1$ to the tens column.

You're adding $47 + 35$. You've carried the $1$ to the tens column. What is Step 3?

Step 3: Add all the digits in the tens column, including the carried-over $1$. $1 + 4 + 3 = 8$.

You're adding $47 + 35$ and have added the tens to get $8$. What is the final step?

Final Step: Write the $8$ in the tens place of the answer. The final sum is $82$.

Solve $58 + 24$. What's the first step?

Add the ones: $8 + 4 = 12$.

You are solving $58 + 24$. After adding the ones to get $12$, what do you do?

Write down the $2$ in the ones place and carry the $1$ to the tens column.

You are solving $58 + 24$. You carried a $1$. What is the sum of the tens column?

Add the tens: $1 + 5 + 2 = 8$.

What is the final answer to $58 + 24$?

$$\begin{array}{rr} & 58 \\ + & 24 \\ \hline & 82 \end{array}$$

Let's try $39 + 45$. What do you get when you add the ones, and what do you do?

$9 + 5 = 14$. Write down the $4$ and carry the $1$.

For $39 + 45$, after carrying the $1$, what is the sum of the tens column?

$1 + 3 + 4 = 8$.

What is the final answer to $39 + 45$?

$$\begin{array}{rr} & 39 \\ + & 45 \\ \hline & 84 \end{array}$$

Let's try $58 + 17$. How to solve this?

$8 + 7 = 15$, so write $5$ to ones and carry the $1$. $5 + 1 + 1 = 7$. The answer is $75$ $$\begin{array}{rr} & 58 \\ + & 17 \\ \hline & 75 \end{array}$$

Solve this $54 + 39$.

$$\begin{array}{rr} & 54 \\ + & 39 \\ \hline & 93 \end{array}$$

Does the order you add the numbers in the tens column matter (e.g., adding the carried $1$ first or last)?

No, because addition is commutative. You can add the numbers in any order and get the same sum. $1+5+2$ is the same as $5+2+1$.