What Number Am I? The “Multiply by 2 and Add 12” Math Riddle Solved
Simple arithmetic riddles and word-problem math puzzles are reliable drivers of viral engagement across social media. They test foundational algebra and reverse-operation logic by presenting basic arithmetic operations as a first-person mystery.
A widely shared text puzzle features the following riddle:
“I’m a number.
Multiply me by 2 and add 12.
You get 30.
What number am I?”
While word problems can sometimes sound confusing at first glance, breaking down the problem into a standard two-step algebraic equation makes the solution simple and straightforward.
In this guide, we translate the riddle into an equation, solve it using two different methods (algebraic substitution and working backwards), and verify the final result.
Deconstructing the Riddle into an Algebraic Equation
To solve the riddle mathematically, let’s represent the unknown number with the variable $x$:
[ RIDDLE TO ALGEBRA TRANSLATION ]
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| | | |
[ UNKNOWN NUMBER ] [ MULTIPLY BY 2 ] [ ADD 12 ] [ EQUALS 30 ]
• Let x = unknown • 2x • 2x + 12 • 2x + 12 = 30
This gives us the linear algebraic equation:
Method 1: Algebraic Step-by-Step Solution
To solve for $x$, isolate the variable by applying inverse operations in reverse order:
Step 1: Subtract 12 from both sides of the equation
Step 2: Divide both sides by 2
Method 2: Working Backwards (Reverse Operations)
If you prefer mental math without setting up formal algebraic variables, you can simply reverse each step described in the riddle starting from the final number (30):
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Start with the final result: $30$
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Reverse “add 12” (Subtract 12):
$$30 – 12 = 18$$ -
Reverse “multiply by 2” (Divide by 2):
$$18 \div 2 = 9$$
Both methods yield the exact same result!
Verification Check
Let’s plug $x = 9$ back into the original riddle prompt to confirm:
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Start with the number: $9$
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Multiply by 2:
$$9 \times 2 = 18$$ -
Add 12:
$$18 + 12 = 30$$
The result matches the prompt (30), confirming the answer is correct.
Summary Table
| Operation Step | Word Problem Prompt | Reverse Math Step | Resulting Value |
| Final Result | “You get 30.” | Starting point | 30 |
| Reverse Addition | “Add 12” | Subtract 12 ($30 – 12$) | 18 |
| Reverse Multiplication | “Multiply me by 2” | Divide by 2 ($18 \div 2$) | 9 |
| Starting Number | “What number am I?” | Isolated Variable ($x$) | 9 |
The Answer
The number is 9.
Common Mistakes & Why Solvers Get Stuck
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Order of Operations Confusion: Some solvers attempt to divide 30 by 2 before subtracting 12, yielding an incorrect answer of $3$ ($(30 \div 2) – 12 = 3$). Always undo additions and subtractions before undoing multiplications.
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Arithmetic Errors: Subtracting 12 from 30 incorrectly (e.g., getting 16 or 20 instead of 18) leads to common miscalculated guesses like 8 or 10 in comment threads.
Conclusion
The correct answer to “What number am I?” is 9. By either undoing the operations backwards ($30 – 12 = 18$, $18 \div 2 = 9$) or solving the linear equation $2x + 12 = 30$, the solution comes together effortlessly!
Frequently Asked Questions (FAQ)
What is the answer to “Multiply me by 2 and add 12. You get 30”?
The answer is 9.
What algebraic equation represents this riddle?
The riddle is represented by the linear equation $2x + 12 = 30$, where $x$ represents the unknown number.
