Solve the Equation: Finding the Missing Number in 800-?=800

Q: Why isn't the answer 800 since it appears twice in the equation?

The fact that 800 appears multiple times is a distraction! We need the number that, when subtracted from 800, gives us 800. Only zero has this special property.

Q: How do I remember the zero property?

Think of it this way: if you have 800 cookies and eat zero cookies, you still have all 800! Subtracting nothing leaves everything unchanged.

Q: What if the equation was 800 - ? = 0 instead?

Then the answer would be 800! You'd need to subtract all of the original amount to get zero. The key is reading what the equation equals on the right side.

Q: Is this the same as adding zero?

Yes! Both $ x + 0 = x $ and $ x - 0 = x $ show that zero is the additive identity - it doesn't change the value when added or subtracted.

Zero Property with Subtraction Operations

$800-?=800$

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Step-by-step video solution

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00:00 Find the unknown

00:03 Any number minus 0 equals the number itself

00:11 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

$800-?=800$

Step-by-step solution

To solve this problem, we must determine which number, when subtracted from 800, results in 800. We can solve this by recognizing certain properties of numbers.

Step 1: Identify the equation $800 - ? = 800$ .
Step 2: Understand that for the equation to hold, the value of '?' must be such that subtracting it leaves 800 unchanged.
Step 3: Recognize that zero has the property $x - 0 = x$ for any number $x$ .

So, substituting zero for '?', we have:
$800 - 0 = 800$ , which is true.

Therefore, the number that satisfies the equation $800 - ? = 800$ is $0$ . The correct choice is therefore option 2.

Final Answer

Key Points to Remember

Essential concepts to master this topic

Identity Property: Subtracting zero from any number leaves it unchanged
Technique: Set up equation $800 - x = 800$ and solve for x
Check: Substitute back: $800 - 0 = 800$ is true ✓

Common Mistakes

Avoid these frequent errors

Thinking the answer must be 800
Don't assume the missing number equals 800 just because it appears in the equation = wrong answer of 800! This gives 800 - 800 = 0, not 800. Always recognize that subtracting zero keeps the original number unchanged.

Practice Quiz

Test your knowledge with interactive questions

$$ 20:1= $$

FAQ

Everything you need to know about this question

Why isn't the answer 800 since it appears twice in the equation?

The fact that 800 appears multiple times is a distraction! We need the number that, when subtracted from 800, gives us 800. Only zero has this special property.

How do I remember the zero property?

Think of it this way: if you have 800 cookies and eat zero cookies, you still have all 800! Subtracting nothing leaves everything unchanged.

What if the equation was 800 - ? = 0 instead?

Then the answer would be 800! You'd need to subtract all of the original amount to get zero. The key is reading what the equation equals on the right side.

Is this the same as adding zero?

Yes! Both $x + 0 = x$ and $x - 0 = x$ show that zero is the additive identity - it doesn't change the value when added or subtracted.

How can I check my answer is definitely right?

Substitute your answer back into the original equation. If you get $800 - 0 = 800$ , and this is true, then zero is correct!

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