Solve the Equation: Finding the Missing Number in 2200 - □ = 2100

Q: How can I do this subtraction quickly?

Think of it as counting backwards! From 2200 to 2100, you go down by exactly 100. You can also break it down: 2200 - 2000 - 100 = 200 - 100 = 100.

Q: What if I get confused about which number to subtract?

Remember: you're looking for the difference between the two numbers. Always subtract the smaller number from the larger number to get a positive result.

Q: How do I check if 100 is really the right answer?

Substitute it back! Replace the box with 100: $ 2200 - 100 = 2100 $. Since this is true, your answer is correct!

Q: Is there another way to think about this problem?

Yes! You can think: "What number do I need to take away from 2200 to get 2100?" The answer is the difference between these two numbers.

Subtraction Equations with Missing Minuends

Complete the following equation:

$2200-\Box=2100$

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Step-by-step written solution

Follow each step carefully to understand the complete solution

Understand the problem

Complete the following equation:

$2200-\Box=2100$

Step-by-step solution

To solve this problem, we need to find the number that, when subtracted from 2200, results in 2100. Let's follow these steps:

Step 1: Recognize that we are solving for the missing number, denoted by $\Box$ , in the equation $2200 - \Box = 2100$ .
Step 2: Rearrange the equation to solve for $\Box$ . The equation can be rewritten as $\Box = 2200 - 2100$ .
Step 3: Perform the subtraction to find $\Box$ . Calculate 2200 minus 2100.

Calculating the subtraction:

$2200 - 2100 = 100$

Therefore, the missing number, $\Box$ , is 100.

In conclusion, the correct answer is $100$ .

Final Answer

$100$

Key Points to Remember

Essential concepts to master this topic

Rearrangement Rule: Transform $a - \Box = b$ into $\Box = a - b$
Mental Math: Calculate 2200 - 2100 by counting down in hundreds
Verification: Check by substituting: 2200 - 100 = 2100 ✓

Common Mistakes

Avoid these frequent errors

Subtracting in wrong order
Don't calculate 2100 - 2200 = -100! This gives a negative answer when the missing number should be positive. Always rearrange first: □ = 2200 - 2100, then subtract the smaller number from the larger number.

Practice Quiz

Test your knowledge with interactive questions

Choose the correct answer:

$693+705=\text{ ?}$

FAQ

Everything you need to know about this question

Why do I need to rearrange the equation first?

Rearranging helps you see exactly what calculation to do! When you change $2200 - \Box = 2100$ to $\Box = 2200 - 2100$ , you know to subtract 2100 from 2200.

How can I do this subtraction quickly?

Think of it as counting backwards! From 2200 to 2100, you go down by exactly 100. You can also break it down: 2200 - 2000 - 100 = 200 - 100 = 100.

What if I get confused about which number to subtract?

Remember: you're looking for the difference between the two numbers. Always subtract the smaller number from the larger number to get a positive result.

How do I check if 100 is really the right answer?

Substitute it back! Replace the box with 100: $2200 - 100 = 2100$ . Since this is true, your answer is correct!

Is there another way to think about this problem?

Yes! You can think: "What number do I need to take away from 2200 to get 2100?" The answer is the difference between these two numbers.

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