ELI5: Explain Like I'm 5

Popoviciu's inequality

Popoviciu's inequality is like a math rule that helps us figure out how numbers work when they're all different from each other. It says that if we have a bunch of numbers (we'll call them X, Y, and Z), and we want to know the biggest and smallest they can be, we can use a special formula to figure it out.

Here’s how it works:

1. We add up all of the numbers: X + Y + Z.
2. We find the average (also called the mean) of the numbers by dividing the sum by 3: (X + Y + Z) / 3.
3. We subtract the average from each number, and we take the absolute value (which means we ignore the negative sign): |X - (X + Y + Z) / 3|, |Y - (X + Y + Z) / 3|, and |Z - (X + Y + Z) / 3|.
4. Then, we add up all of those absolute values and divide by 3: (|X - (X + Y + Z) / 3| + |Y - (X + Y + Z) / 3| + |Z - (X + Y + Z) / 3|) / 3.
5. Finally, the biggest number is the average plus that result, and the smallest number is the average minus that result.

It might seem complicated, but it's actually really helpful when we want to know things like the biggest and smallest temperatures we might experience in a week, or the fastest and slowest speeds a car might go. Popoviciu's inequality just helps us figure it all out using math.