ELI5: Explain Like I'm 5

Archimedes's cattle problem

Hi there! Today I am going to tell you about a really tricky math problem that was invented by a famous scientist named Archimedes. This problem is called Archimedes's cattle problem. Are you ready to learn more?

Okay, so let's say you are a farmer and you have a big field where you keep your cows. You know how many cows you have, but what if you didn't? What if you wanted to figure out exactly how many cows you had without counting them one by one?

That's where Archimedes's problem comes in. He came up with a special formula that can help you figure out the exact number of cows you have in your field.

But this is no ordinary formula. It involves something called quadratic equations, which are a lot more complicated than regular math problems. So let me explain it to you step by step.

First, you need to know how many different types of cows you have in your field. Let's say you have two types: white cows and black cows. And you know that together they have a total of 100 feet (because cows have four legs, and 4 x the number of cows is the same as the total number of feet they have).

Next, you need to know how many pairs of cows there are. You might be thinking, "But I don't know how many cows I have!" That's okay. Archimedes's formula uses a special type of guessing, called a "trial and error" method.

You start by guessing. Let's say you guess that there are 10 pairs of cows in your field. That's 20 cows total. Now, using the fact that you have 100 feet in total, you can figure out how many feet are white cows and how many are black cows.

Here's another tricky part: Archimedes's formula requires you to use a bunch of different equations to figure out how many feet belong to each type of cow. These equations are called "quadratic equations" because they involve the square of a number (like 4 x 4 = 16). Don't worry if you don't understand everything right away. It's a very complicated problem!

After using the quadratic equations, you might find that the number of feet you calculated for the white cows is higher than the actual number of feet you counted earlier. So you need to adjust your guess. You can try with 11 pairs of cows. And then keep adjusting until you find the right answer!

Eventually, if you keep guessing and adjusting, you will find a number of pairs of cows that satisfies all the equations and gives you the right number of feet overall. And that's how you can use Archimedes's cattle problem to figure out how many cows you have in your field!

So there you have it, the explanation about Archimedes's cattle problem in a way that a 5-year-old could understand. It's a tricky problem, but it's really cool that people like Archimedes could come up with such clever solutions to complicated math questions.