Solve the Subtraction Problem: 99 Minus 9

Q: Why do I get confused about which number to subtract from which?

In vertical subtraction, always subtract the bottom number from the top number. The larger number (99) goes on top, and you subtract the smaller number (9) from it.

Q: How do I know if I aligned the numbers correctly?

Make sure the rightmost digits line up first! The 9 in the bottom should be directly under the 9 in the ones place of 99, not under both digits.

Q: Can I solve this problem using a different method?

Yes! You can think of it as 99 - 9 = 90 using mental math. Since 90 + 9 = 99, we know 99 - 9 = 90.

Q: What if I get 88 or 98 as my answer?

These are common mistakes! Check by adding: Does 88 + 9 = 99? No, it equals 97. Does 98 + 9 = 99? No, it equals 107. Only 90 + 9 = 99.

Subtraction with Two-Digit Numbers

$\begin{aligned} &99 \\ -& \\ &~~9 \\ &\underline{\phantom{776}} & \\ \end{aligned}$

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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 consider a subtraction of 2 digits, and then we'll write

00:06 Let's start by subtracting ones from ones, and write in the ones place

00:09 Write 0 in the missing digits

00:13 Subtract tens from tens, and write in the tens place

00:16 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

$\begin{aligned} &99 \\ -& \\ &~~9 \\ &\underline{\phantom{776}} & \\ \end{aligned}$

Step-by-step solution

To solve this problem, let's perform vertical subtraction:

Step 1: Align the numbers 99 and 9 for subtraction.
Step 2: Subtract starting from the rightmost digits: the ones place.
Step 3: $9 - 9 = 0$ in the ones place.
Step 4: Move to the tens place: $9 - 0 = 9$ . (Since we did not borrow any value from the tens place, the 9 remains.)

Thus, the result of the subtraction is $90$ .

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

Final Answer

Key Points to Remember

Essential concepts to master this topic

Alignment: Place ones under ones, tens under tens for accuracy
Technique: Start from right: 9 - 9 = 0, then 9 - 0 = 9
Check: Add your answer to the smaller number: 90 + 9 = 99 ✓

Common Mistakes

Avoid these frequent errors

Subtracting larger digit from smaller digit
Don't subtract 9 from 0 in the tens place = negative result! When subtracting 9 from 99, the 9 aligns under the ones place, leaving the tens digit unchanged. Always align digits properly by place value.

Practice Quiz

Test your knowledge with interactive questions

$\begin{aligned} &97 \\ -& \\ &63 \\ &\underline{\phantom{776}} & \\ \end{aligned}$ $$

FAQ

Everything you need to know about this question

Why do I get confused about which number to subtract from which?

In vertical subtraction, always subtract the bottom number from the top number. The larger number (99) goes on top, and you subtract the smaller number (9) from it.

What happens when there's no digit in the tens place of the bottom number?

When 9 is written under 99, think of it as 09. The tens place has a 0, so you subtract 0 from 9, which gives you 9.

How do I know if I aligned the numbers correctly?

Make sure the rightmost digits line up first! The 9 in the bottom should be directly under the 9 in the ones place of 99, not under both digits.

Can I solve this problem using a different method?

Yes! You can think of it as 99 - 9 = 90 using mental math. Since 90 + 9 = 99, we know 99 - 9 = 90.

What if I get 88 or 98 as my answer?

These are common mistakes! Check by adding: Does 88 + 9 = 99? No, it equals 97. Does 98 + 9 = 99? No, it equals 107. Only 90 + 9 = 99.

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