Solve Vertical Addition: 81 Plus 9 Step-by-Step

Q: Why do I need to carry when adding 1 + 9?

Because 1 + 9 = 10, which is a two-digit number! In the units place, you can only write single digits (0-9). So you write the 0 and carry the 1 to the tens place.

Q: What does 'carry' actually mean?

Carrying means moving extra value to the next place value column. When you get 10 ones, that equals 1 ten, so you move that 1 to the tens column.

Q: How do I know when to carry?

Carry whenever the sum in any column is 10 or greater. Write the ones digit in that column and carry the tens digit to the next column left.

Q: Can I add from left to right instead?

It's possible but much harder! Adding from right to left (units to tens) is easier because you handle carrying as you go, making fewer mistakes.

Vertical Addition with Carrying Strategy

$\begin{aligned} &81 \\ +& \\ &~~9 \\ &\underline{\phantom{776}} & \\ \end{aligned}$

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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 calculate the sum of 2 digits, and then place

00:06 Let's start by adding ones with ones

00:09 Place the ones, add the tens to the tens

00:12 Remember 1 carry over

00:15 Place 0 where there is no digit

00:18 Add tens with tens, remember to add 1

00:21 Place the solution in tens

00:24 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

$\begin{aligned} &81 \\ +& \\ &~~9 \\ &\underline{\phantom{776}} & \\ \end{aligned}$

Step-by-step solution

The problem is to perform vertical addition for the numbers $81$ and $9$ . Here’s the step-by-step approach:

Step 1: Align the numbers vertically by their rightmost digits. The digit $1$ from $81$ is aligned with $9$ .
Step 2: Add the digits in the units place: $1 + 9 = 10$ . Here, $10$ is a two-digit result, where $0$ remains in the units place and $1$ is carried to the tens place.
Step 3: Add the digits in the tens place, including the carried digit: $8 + 1 = 9$ . This accounts for the $1$ we carried over from the units place addition.

Since no further carrying is necessary, the result of adding $81$ and $9$ is $90$ .

Therefore, the solution to the problem is $90$ , which corresponds to choice 2.

Final Answer

Key Points to Remember

Essential concepts to master this topic

Alignment: Line up digits by place value, units under units
Carrying: When sum exceeds 9, write ones digit and carry tens
Verification: Check by adding horizontally: 81 + 9 = 90 ✓

Common Mistakes

Avoid these frequent errors

Forgetting to carry the 1 to tens place
Don't write 10 in the units column = wrong answer like 810! When 1 + 9 = 10, you must write 0 in units and carry 1 to tens. Always carry any digit above 9 to the next place value.

Practice Quiz

Test your knowledge with interactive questions

$\begin{aligned} &83 \\ +& \\ &~~6 \\ &\underline{\phantom{776}} & \\ \end{aligned}$

FAQ

Everything you need to know about this question

Why do I need to carry when adding 1 + 9?

Because 1 + 9 = 10, which is a two-digit number! In the units place, you can only write single digits (0-9). So you write the 0 and carry the 1 to the tens place.

What does 'carry' actually mean?

Carrying means moving extra value to the next place value column. When you get 10 ones, that equals 1 ten, so you move that 1 to the tens column.

How do I know when to carry?

Carry whenever the sum in any column is 10 or greater. Write the ones digit in that column and carry the tens digit to the next column left.

Can I add from left to right instead?

It's possible but much harder! Adding from right to left (units to tens) is easier because you handle carrying as you go, making fewer mistakes.

What if I forget to add the carried number?

You'll get the wrong answer! In this problem, forgetting the carried 1 would give you $80 + 9 = 89$ instead of the correct $90$ . Always remember to add carried digits!

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