Solve Vertical Subtraction: 72 minus 8 Step-by-Step

Q: Why can't I just subtract 8 from 2 directly?

You can't subtract a larger number from a smaller one and get a positive result! Since 2 is smaller than 8, you need to borrow from the tens place first.

Q: How do I know when I need to borrow?

Look at each column from right to left. If the top digit is smaller than the bottom digit, you need to borrow from the next column to the left.

Q: What happens to the tens digit when I borrow?

The tens digit goes down by 1 because you're lending one group of 10 to the units place. So 7 becomes 6, and the units place gets 10 more (2 + 10 = 12).

Q: How can I check if my subtraction is correct?

Add your answer to the number you subtracted. If you get the original number, you're right! For example: $64 + 8 = 72$ ✓

Q: What if there's a zero in the tens place?

If you need to borrow from a zero, you'll need to borrow from the hundreds place first, making the zero become 10, then borrow 1 from that to help the units place.

Q: Is there an easier way to do 72 - 8?

You could think: 72 - 10 = 62, then 62 + 2 = 64. But learning the borrowing method helps with harder problems where mental math isn't as easy!

Vertical Subtraction with Borrowing

$\begin{aligned} &72 \\ -& \\ &~~8 \\ &\underline{\phantom{776}} & \\ \end{aligned}$

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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 calculate a subtraction of 2 digits, and then we substitute

00:06 4 is less than

00:09 Therefore we'll subtract 1 from the tens, and add this sum to the ones

00:14 Meaning now instead of 4 we'll have 14

00:19 We subtract the ones from the ones plus ten

00:22 We substitute in the ones place

00:25 We put 0 in the missing digits

00:28 We subtract tens from tens, and substitute in the tens place

00:31 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

$\begin{aligned} &72 \\ -& \\ &~~8 \\ &\underline{\phantom{776}} & \\ \end{aligned}$

Step-by-step solution

Let us solve the subtraction problem $72 - 8$ step-by-step.

1. Write the numbers vertically, ensuring that the digits are aligned by place value:

72
- 8
$\underline{\phantom{776}}$

2. Subtract the digits in the units column:

Since $2$ is smaller than $8$ , we need to borrow from the tens column.
Adjust the tens digit from $7$ to $6$ (because we borrow 10 from it) and make the units digit $2 + 10 = 12$ .

3. Now perform the subtraction for the units column:

Subtract $8$ from $12$ , which equals $4$ .

4. Now, focus on the tens column:

Subtract the adjusted tens digit, $6$ , from $0$ (as there is no digit under it in the subtrahend), resulting in $6$ .

5. This gives us the final answer:

The result of $72 - 8$ is $\mathbf{64}$ .

Therefore, the solution to the problem is $64$ .

Final Answer

Key Points to Remember

Essential concepts to master this topic

Alignment: Stack numbers by place value, units under units
Borrowing: When 2 < 8, borrow 10 from tens column
Check: Add your answer to subtrahend: 64 + 8 = 72 ✓

Common Mistakes

Avoid these frequent errors

Forgetting to adjust the tens digit after borrowing
Don't just add 10 to the units place and leave 7 in tens = wrong answer like 74! This ignores that you borrowed 1 ten from the tens column. Always reduce the tens digit by 1 after borrowing.

Practice Quiz

Test your knowledge with interactive questions

$\begin{aligned} &15 \\ -& \\ &~~4 \\ &\underline{\phantom{776}} & \\ \end{aligned}$

FAQ

Everything you need to know about this question

Why can't I just subtract 8 from 2 directly?

You can't subtract a larger number from a smaller one and get a positive result! Since 2 is smaller than 8, you need to borrow from the tens place first.

How do I know when I need to borrow?

Look at each column from right to left. If the top digit is smaller than the bottom digit, you need to borrow from the next column to the left.

What happens to the tens digit when I borrow?

The tens digit goes down by 1 because you're lending one group of 10 to the units place. So 7 becomes 6, and the units place gets 10 more (2 + 10 = 12).

How can I check if my subtraction is correct?

Add your answer to the number you subtracted. If you get the original number, you're right! For example: $64 + 8 = 72$ ✓

What if there's a zero in the tens place?

If you need to borrow from a zero, you'll need to borrow from the hundreds place first, making the zero become 10, then borrow 1 from that to help the units place.

Is there an easier way to do 72 - 8?

You could think: 72 - 10 = 62, then 62 + 2 = 64. But learning the borrowing method helps with harder problems where mental math isn't as easy!

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