Digit Manipulation: Changing Units (+7) and Tens (-8) in 191

Q: How do I remember which digit is which in a three-digit number?

Use this trick: read from right to left! The rightmost digit is always units, middle is tens, leftmost is hundreds. In 191: 1 (hundreds), 9 (tens), 1 (units).

Q: Why don't we change the hundreds digit?

The problem only asks us to change the units and tens digits. The hundreds digit stays the same unless specifically mentioned. Always read the instructions carefully!

Q: How can I check my answer is correct?

Compare your final number digit by digit: Original 191 → Final 118. Units: 1+7=8 ✓, Tens: 9-8=1 ✓, Hundreds: unchanged 1 ✓

Place Value Manipulation with Three-Digit Numbers

Increase the units digit in the number 191 by 7 and decrease its tens digit by 8.

What is the resulting number?

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Step-by-step written solution

Follow each step carefully to understand the complete solution

Understand the problem

Increase the units digit in the number 191 by 7 and decrease its tens digit by 8.

What is the resulting number?

Step-by-step solution

To solve the problem, we will focus on these steps:

Step 1: Identify the digits of the number 191.
The number 191 consists of:
- Units digit: 1
- Tens digit: 9
- Hundreds digit: 1
Step 2: Increase the units digit by 7.
The units digit is 1. Adding 7 results in 8.
Step 3: Decrease the tens digit by 8.
The tens digit is 9. Subtracting 8 gives 1.
Step 4: Reconstruct the new number using the modified digits.
The modified digits are:
- Units digit: 8
- Tens digit: 1
- Hundreds digit (unchanged): 1
Thus, the new number is $118$ .

Therefore, the resulting number after these changes is $118$ .

Final Answer

$118$

Key Points to Remember

Essential concepts to master this topic

Place Value: Identify units, tens, and hundreds positions in numbers
Technique: Units digit 1 + 7 = 8, tens digit 9 - 8 = 1
Check: Verify final digits match calculations: 118 has units 8, tens 1 ✓

Common Mistakes

Avoid these frequent errors

Confusing tens and units digit positions
Don't mix up which digit is which = wrong final answer! Students often change the wrong digits because they misidentify place values. Always identify units (rightmost), tens (middle), hundreds (leftmost) before making changes.

Practice Quiz

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FAQ

Everything you need to know about this question

How do I remember which digit is which in a three-digit number?

Use this trick: read from right to left! The rightmost digit is always units, middle is tens, leftmost is hundreds. In 191: 1 (hundreds), 9 (tens), 1 (units).

What if adding or subtracting makes a digit negative or over 9?

Great question! In this problem, 9 - 8 = 1 and 1 + 7 = 8, so we stay between 0-9. If you got a negative number or over 9, you'd need borrowing or carrying.

Why don't we change the hundreds digit?

The problem only asks us to change the units and tens digits. The hundreds digit stays the same unless specifically mentioned. Always read the instructions carefully!

How can I check my answer is correct?

Compare your final number digit by digit: Original 191 → Final 118. Units: 1+7=8 ✓, Tens: 9-8=1 ✓, Hundreds: unchanged 1 ✓

What's the easiest way to do this type of problem?

Follow these steps: 1) Write down the original number, 2) Identify each digit's position, 3) Do the math for each change, 4) Write the new number with changed digits.

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