There are 10,000 possible combinations of four numbers when each number is used numerous times. There are also 5,040 possible four-number combinations when each number is used only once.

How so? There are ten options, ranging from zero to nine, for each number in the combination. Due to the fact that there are four numbers in the combination, there are a total of 10 possible combinations for each of the four numbers. Thus, the number of viable possibilities is 10*10*10*10 or 104, or 10,000.

The formula for the binomial coefficient is a general method for calculating the number of combinations. The number of combinations of k items from a collection of n elements is denoted by n!/(k!*(n-k)!, where the exclamation mark signifies a factorial. Need to go into greater detail? We have you covered.

## Formula for Combination count

A straightforward equation can be utilised to determine the number of possible four-number combinations. Consider each number as an individual and each position in the combination as a seat. Each seat can only accommodate one person, and there are a total of 10 seats available. (There are ten numbers since numbers with a single digit range from 0 to 9)

In each given combination, any of the ten numbers can occupy any of the four available positions. There are ten alternatives for the first seat in every given combination. In addition, there are 10 alternatives for the second seat in each given combination. The same holds true for the third and fourth seats as well. Multiply the number of possibilities for the first seat by the number of options for the second seat by the number of options for the third seat by the number of options for the fourth seat to find the total number of alternatives for all combinations.

In other words, multiply 10 by 10 by 10 by 10 by 10. You will ultimately discover that there are 10,000 different combinations of four numbers.

## Number of Combinations Formulas for Non-Repetitive Numbers.

If you claim that there are 10,000 possible four-number combinations, you would be both correct and incorrect. Thus, the answer of 10,000 allows any of the ten numbers to occupy any of the four seats. One of the 10,000 possible combinations may be 1111, 0000, 2222, or 3333, according to this theory. Let’s add a twist to the equation.

In the actual world, four-digit combinations are typically devoid of repeated digits. In fact, several companies prohibit the use of four-digit passwords that consist of repeated numbers. How many possible four-digit number combinations do not contain repeated digits?

Forget about the chairs for a while and consult the binomial coefficient formula, a handy mathematical formula. The following is the formula:

n!/(k! x (n-k)!)

In case you were unaware, each exclamation point denotes a factorial. Although both the term and the formula appear to be difficult, the process is actually quite simple. It turns out that the concept of persons seated will also be useful here. “K” represents the number of persons who can sit in any given seat, and “n” represents the number of seats each of those people can occupy.

In the case of determining the number of combinations of four numbers, k equals 10 and n equals 4. The equation is as follows:

4!/(10! x (4-10)!)

## Without entering into factorials, this reduces to:

10 x 9 x 8 x 7 = 5,040

Do you detect a pattern here? Any one of the ten numbers may occupy the first available seat. Now, only nine numbers remain to occupy the second slot. With one more number eliminated, there are only eight remaining candidates for the third seat, and only seven candidates for the fourth slot.

See? The binomial coefficient is much easy than it initially appears. With the binomial coefficient, any number selected for one seat is eliminated from consideration for the remaining seats. This almost half the overall number of possible combinations.

## What This Reveals About Your Mobile Device Password

Let’s be honest. Unless you’re extremely interested in numbers, you probably didn’t look for the number of possible four-digit combinations. In all likelihood, you have landed on this page because you are attempting to create a four-digit password. And it is excellent that you are considering your passcode.

Since they are among the shortest passwords you’re likely to use, four-digit passwords can appear to be rather straightforward. However, they are frequently among the most significant. You may use four-digit number combinations to fast unlock your phone or log into particular applications, but where else do you utilise them? The majority of banks require consumers to choose a four-digit PIN to approve transactions and use ATMs.

Hackers take advantage of the fact that four-digit number combinations are used as passwords for items that you care significantly less about securing than your bank card PIN. People are not nearly as creative with passwords as they ought to be. If someone can decipher the code on your phone’s lock screen, it’s likely that they can also authorise a transaction using your debit card, as there’s a strong likelihood that the numbers are identical.

Banks don’t help the problem either. Oftentimes, people have 10,000 choices when it comes to PINs because many banks will allow for repeating numbers. If your bank is a little more security savvy, you’ll only have 5,040 combinations to choose from. Many people use four-digit combinations that are either repetitive or in sequential order. For example, 1234 is a very common choice, and other people combine the same number over and over, such as 1111 or 2222.

Don’t let your knowledge of the binomial coefficient go to waste. There are literally thousands of combinations of four numbers that you could choose from. Do not just pick your birth year or your birth date. For the love of all that is good, please don’t pick 1234 either. If you want to keep a certain someone’s prying eyes out of your smartphone, you’re going to have to try way harder than that. Choose your passwords wisely and keep your identity (and information) safe.