ELI5: Explain Like I'm 5

Sylvester's formula

Sylvester's formula is an equation that's used to help figure out the number of different ways to arrange a set of items. For example, if you have 5 balls, the formula can help tell you how many different ways you can arrange them. To understand the equation you'll need to know a few math terms, so here's a brief explanation.

First, you need to know the factorial of a number. The factorial of a number is the product of all the numbers from 1 to that number. For example, the factorial of 5 is 1 x 2 x 3 x 4 x 5, which is equal to 120.

Once you know the factorial of a number, you'll need to know how to find a combination. A combination is when you take a certain number of items from a larger group. For example, if you have 5 balls you can take 2 of them, but you don't care about which 2 you take. The formula for combinations is the factorial of the larger number (5 in the case of 5 balls) divided by the product of the factorial of the smaller number (2 in this case) and the factorial of the difference between the larger and smaller numbers (in this case, 3). So for 5 balls you'll get 5!/ (2! x 3!), which is equal to 10.

Sylvester's formula is actually a combination of this formula and another formula called the permutation formula. The permutation formula is used to figure out how many different ways you can arrange a set of items. For example, if you have 5 balls, you can arrange them in 5 different ways. The formula is the factorial of the number of items (in this case, 5). So for 5 balls you'll get 5!, which is equal to 120.

Now, back to Sylvester's formula. This formula is used to figure out how many different ways you can arrange a set of items with a certain number taken from the set. For example, if you have 5 balls and you want to figure out how many different arrangements you can make with 2 of them, then Sylvester's formula is the way to go. To use the formula, you'll first calculate the combination using the formula above (5!/ (2! x 3!)). Then you'll take that number (10 in this case) and multiply it by the permutation formula (5!) to get the final number of different arrangements of 2 balls that you can have from the set of 5 (120 in this case). So, in this example, Sylvester's formula gives you the answer that there are 120 different arrangements of 2 balls you can have from a set of 5.
Related topics others have asked about: