Solve Vertical Addition: 81 + 8 Step by Step

Q: Why do I need to align the numbers by place value?

Place value alignment ensures you're adding the right digits together! The 8 goes under the 1 (ones column), not under the 8 (tens column). This keeps your addition accurate.

Q: What if I accidentally put 8 under the tens column?

You'd be adding $ 81 + 80 = 161 $ instead of $ 81 + 8 = 89 $! Always check that single-digit numbers go in the ones column.

Q: Do I always start adding from the right side?

Yes! Always start from the ones column (rightmost) and work left. This is important for carrying over when sums exceed 9.

Q: How can I double-check my vertical addition?

Try the same problem horizontally: $ 81 + 8 $. If you get the same answer both ways, you're correct!

Vertical Addition with Place Value Alignment

$\begin{aligned} &81 \\ +& \\ &~~8 \\ &\underline{\phantom{776}} & \\ \end{aligned}$

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations

00:00 Solve

00:03 Each time we consider combining 2 digits, and then we'll place

00:06 We'll start by combining ones with ones, we'll place the solution

00:09 We'll place 0 where there is no digit

00:12 We'll combine tens with tens, we'll place the solution

00:15 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution

Understand the problem

$\begin{aligned} &81 \\ +& \\ &~~8 \\ &\underline{\phantom{776}} & \\ \end{aligned}$

Step-by-step solution

To solve the given vertical addition problem, follow these steps:

Step 1: Align the numbers by place value: 81 has a tens digit (8) and a ones digit (1). The number 8 is placed under the ones digit.
Step 2: Start with the ones column: Add the digits $1 + 8$ . The sum of 1 and 8 is 9.
Step 3: Since the sum in the ones column is less than 10, there is no need to carry over a number to the tens column.
Step 4: Move to the tens column: There is no additional number under the 8, so it remains as 8.
Step 5: Combine these results to get the final sum: The tens digit is 8 and the ones digit is 9, resulting in the number 89.

Therefore, the solution to the problem is $89$ .

Final Answer

Key Points to Remember

Essential concepts to master this topic

Alignment: Line up digits by place value columns correctly
Technique: Start from ones column: $1 + 8 = 9$
Check: Verify by horizontal addition: $81 + 8 = 89$ ✓

Common Mistakes

Avoid these frequent errors

Misaligning digits in the wrong columns
Don't place 8 under the tens digit of 81 = wrong alignment gives 88 or 90! This happens when you don't match place values properly. Always align the ones digit of 8 under the ones digit of 81.

Practice Quiz

Test your knowledge with interactive questions

$\begin{aligned} &90 \\ +& \\ &~~9\\ &\underline{\phantom{776}} & \\ \end{aligned}$

FAQ

Everything you need to know about this question

Why do I need to align the numbers by place value?

Place value alignment ensures you're adding the right digits together! The 8 goes under the 1 (ones column), not under the 8 (tens column). This keeps your addition accurate.

What if I accidentally put 8 under the tens column?

You'd be adding $81 + 80 = 161$ instead of $81 + 8 = 89$ ! Always check that single-digit numbers go in the ones column.

Do I always start adding from the right side?

Yes! Always start from the ones column (rightmost) and work left. This is important for carrying over when sums exceed 9.

How can I double-check my vertical addition?

Try the same problem horizontally: $81 + 8$ . If you get the same answer both ways, you're correct!

What if there's no carrying needed like in this problem?

That makes it easier! When each column sum is less than 10, simply write the sum in that column. No extra steps needed.

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