Solve Symbol Addition: Finding ○ + 21 When ○ = 7

Symbol Substitution with Basic Addition

If

=7 \circ=7

Solve the following addition problem:

+21= \circ+21=

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Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

If

=7 \circ=7

Solve the following addition problem:

+21= \circ+21=

2

Step-by-step solution

To solve this problem, we'll follow these steps:

  • Step 1: Identify the number represented by the symbol \circ .
  • Step 2: Substitute the symbol \circ with the number 7.
  • Step 3: Perform the addition of 7 and 21.

Now, let's work through each step:
Step 1: Identify =7 \circ = 7 from the problem statement.
Step 2: Substitute the value 7 for \circ in +21 \circ + 21 , so we have 7+21 7 + 21 .
Step 3: Add 7 and 21 to get 28.

Therefore, the solution to the problem is 28 28 .

3

Final Answer

28 28

Key Points to Remember

Essential concepts to master this topic
  • Substitution Rule: Replace the symbol with its given numerical value
  • Technique: Change +21 \circ + 21 to 7+21 7 + 21 when =7 \circ = 7
  • Check: Verify that 7+21=28 7 + 21 = 28 using mental math or counting ✓

Common Mistakes

Avoid these frequent errors
  • Adding the symbol value to the wrong number
    Don't add 7 + 7 = 14 or ignore the substitution completely! This happens when students forget to substitute the symbol or confuse which numbers to add. Always substitute first, then perform the exact addition shown: 7 + 21 = 28.

Practice Quiz

Test your knowledge with interactive questions

If we have 85 blocks in total, how many blocks will remain if we remove 4 tens and 1 one?

FAQ

Everything you need to know about this question

What does the circle symbol represent?

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The circle symbol \circ is just a placeholder for a number! In this problem, it represents the number 7. Think of it like a mystery box that contains the value 7.

Why can't I just add 21 + 21?

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Because the circle \circ doesn't equal 21 - it equals 7! You must substitute the correct value. Always read what the symbol equals first.

How do I know which number goes where?

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Look at the equation carefully: +21 \circ + 21 . The circle comes first, so substitute 7 in the first position: 7 + 21, not 21 + 7 (though addition gives the same result).

What if the symbol had a different value?

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The process stays the same! If =10 \circ = 10 , then +21=10+21=31 \circ + 21 = 10 + 21 = 31 . Always substitute first, then calculate.

Is this the same as solving for x?

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Not quite! Here, we're told what \circ equals (7), so we just substitute and calculate. Solving for x means finding an unknown value through algebraic steps.

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