Mathematical puzzles involving basic arithmetic operations often go viral online because they highlight how easily order of operations (PEMDAS/BODMAS) can be misunderstood. When standard mathematical conventions are ignored, simple expressions yield wildly different answers.
In the classroom image above titled “WHO’S CORRECT?”, a teacher presents the arithmetic expression:
Five students hold up signs with different proposed answers:
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Student 1: 100
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Student 2: 0
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Student 3: 99
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Student 4: 9
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Student 5: 10
In this guide, we break down the correct mathematical solution step-by-step and explain why the answer 99 is mathematically correct.
Order of Operations Breakdown
+--------------------------------------------------------+
| Order of Operations (PEMDAS/BODMAS) |
+---------------------------+----------------------------+
|
v
+--------------------------------------------------------+
| Step 1: Multiplication & Division (Left to Right) |
| - Perform: 10 * 10 = 100 |
| - Perform: 10 / 10 = 1 |
+---------------------------+----------------------------+
|
v
+--------------------------------------------------------+
| Step 2: Subtraction |
| - Subtract: 100 - 1 = 99 |
+--------------------------------------------------------+
The Correct Step-by-Step Calculation
According to the standard order of operations (PEMDAS: Parentheses, Exponents, Multiplication & Division, Addition & Subtraction):
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Multiplication First: Perform $10 \times 10 = 100$.
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Division Next: Perform $10 \div 10 = 1$.
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Subtraction Last: Subtract the result of division from the result of multiplication: $100 – 1 = 99$.
Therefore, the student holding the sign “I got 99” is correct!
Analysis of Student Misconceptions
| Proposed Answer | Method / Calculation Error | Verdict |
| 99 | Applied PEMDAS correctly: $(10 \times 10) – (10 \div 10) = 100 – 1$ | CORRECT |
| 100 | Ignored division entirely or rounded incorrectly | Incorrect |
| 0 | Calculated $(10 \times 10 – 10) \div 10 = (100 – 10) \div 10 = 90 \div 10$ then subtracted wrongly | Incorrect |
| 9 | Worked left to right inconsistently: $(10 \times 10 – 10) \div 10 = 90 \div 10 = 9$ | Incorrect |
| 10 | Misapplied grouping or cancelled terms incorrectly | Incorrect |
Math Skills, Education, and Daily Application
Mastering fundamental math principles builds critical problem-solving skills that apply far beyond classroom riddles.
Developing analytical logic actively enhances cognitive health and mental sharpness. Strong quantitative skills benefit professionals across analytics, marketing, and digital business sectors, helping individuals make sound financial decisions regarding personal finance and budgeting as they prepare for retirement.
Key Takeaways for Order of Operations
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Follow PEMDAS / BODMAS: Always complete multiplication and division before addition and subtraction.
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Work Left to Right: When operations share equal priority (e.g., multiplication and division), evaluate them from left to right.
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Use Parentheses for Clarity: Writing the expression as $(10 \times 10) – (10 \div 10)$ eliminates ambiguity immediately.
Conclusion
Understanding the rules of arithmetic shows that the student who answered 99 is the only one who calculated the problem correctly!
Did you get 99 on your first attempt? Share your thoughts in the comments below!
FAQ Section
What does PEMDAS stand for?
PEMDAS stands for Parentheses, Exponents, Multiplication, Division, Addition, and Subtraction—the order used to solve mathematical expressions.
Why do left-to-right calculations fail here?
Calculating strictly from left to right ignores operator precedence rules, which dictate that multiplication and division must occur prior to subtraction.
