# Ten is Twenty

Algebra Level 1

Here is a proof that $10 = 20:$

Step 1: Consider the system of equations $2x + 4y = 20 \\ x + 2 y = 5.$ Step 2: We can rewrite the second equation as $x = 5 - 2y.$ Step 3: Now, plugging $x=5 - 2y$ into the first equation, we get $2(5-2y) + 4y = 20.$ Step 4: Simplifying, we have $10 - 4y + 4y = 20.$ Step 5: Cancelling out the two $4y$'s, we get $10 = 20.$

Where did the proof go wrong?

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