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The Viral Math Meme: 9 + 10 = 21 Explained

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The Viral Math Meme: 9 + 10 = 21

Have you seen the meme that says 9 + 10 = 21? It’s been making the rounds on social media, and it’s a fun little brain teaser that can be solved with a bit of understanding about different number bases.

The meme is a play on the way we typically think about numbers. We use a base-10 system, which means we have ten digits (0-9) and each place value is ten times greater than the one to its right. So, the number 123 is actually 1 hundred, 2 tens, and 3 ones.

Understanding Number Bases

However, there are other number bases, and one of the most common is base-2, also known as binary. In binary, we only have two digits (0 and 1) and each place value is twice as large as the one to its right. This is the system that computers use to store and process information.

For example, the number 101 in binary is equivalent to 5 in base-10. Here’s how that works:

  • The rightmost digit is a 1, which represents 20 = 1
  • The middle digit is a 0, which represents 21 = 2
  • The leftmost digit is a 1, which represents 22 = 4

So, 101 in binary is equal to 1 + 0 + 4 = 5 in base-10.

Solving the Meme

Now, let’s go back to the meme. The equation 9 + 10 = 21 isn’t true in base-10, but it can be true in a different number base. In fact, it’s true in base-4! Here’s why:

  • 9 in base-10 is equivalent to 21 in base-4 (2 x 41 + 1 x 40 = 8 + 1 = 9)
  • 10 in base-10 is equivalent to 22 in base-4 (2 x 41 + 2 x 40 = 8 + 2 = 10)
  • 21 in base-10 is equivalent to 111 in base-4 (1 x 42 + 1 x 41 + 1 x 40 = 16 + 4 + 1 = 21)

Therefore, in base-4, the equation 21 + 22 = 111 is true, which is the same as 9 + 10 = 21 in base-10.

The Takeaway

This meme is a fun way to illustrate the concept of different number bases. While we typically use base-10 in our everyday lives, other bases are used in different contexts, such as in computers and scientific calculations. Understanding these different bases can help us appreciate the flexibility and power of mathematics.

So next time you see this meme, don’t just laugh it off. Take a moment to think about the different ways we can represent numbers, and how a simple equation can have a different meaning depending on the number base we’re using.

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