Combination Calculator (nCr, nPr) (2024)




nCr =n!
(n-r)! r!

Combinations Formulas

nCr formula

Number of combinations
without repetitions
= nCr
=n!
(n-r)! r!

Combinations with
repetitions formula

Number of combinations
with repetitions
=(n+r-1)!
(n-1)! r!

Permutations Formulas

nPr formula

Number of permutations
without repetitions
= nPr
=n!
(n-r)!

Permutations with
repetitions formula

Number of permutations
with repetitions
= nr

Combinations Calculator

What is a Combination?

A combination is a selection of r items from a set of n items such that we don't care about the order of selection.

Examples of Combinations

Combinations without repetitions

Let's say that we wanted to pick 2 balls out of a bag of 3 balls colored red (R), green (G) and purple (P).
How many unique combinations will we have if we cannot repeat balls?

3 different ways. Our options are: RG, RP and GP.

We can count the number of combinations without repetition using the nCr formula, where n is 3 and r is 2.

# combinations =n!=3!=6= 3
(n-r)!r!2!*1!2

We can see examples of this type of combinations when selecting teams for a sports game or for an assignment. We cannot select a team member more than once (so we can't have a team with Danny, Danny and myself) and we do not care about who is selected first to the team (so if I am in a team with Bob and Tom it is the same to me as being in a team with Tom and Bob).

Combinations with repetitions

Let's say that we wanted to pick 2 balls out of a bag of 3 balls, colored red (R), green (G) and purple (P)
If each time we select a ball we place it back in the bag, how many unique combinations will we have?

6 different ways. Our options are: RR, RG, RP, GG, GP and PP.

We can count the number of combinations with repetitions mathematically by using the combinations with repetitions formula where n = 3 and r = 2.

# combinations =(n+r-1)!=4!=24= 6
(n-1)!r!(3-1)!2!4

We can see examples of this type of combinations when buying ice cream at an ice cream store since we can select flavors more than once (I could get two, three or even four scoops of chocolate ice cream if I wished) and I don't care about which scoop goes on top (so chocolate on top and vanilla on the bottom is the same to me as vanilla on top with a chocolate base).

Permutations Calculator

What is a permutation?

A permutation is a selection of r items from a set of n items where the order we pick our items matters.

Examples of permutations

Permutations without repetitions

Let's say that we wanted to pick 2 balls out of a bag of 3 balls colored red (R), green (G) and purple (P)
How many unique permutations will we have if we cannot repeat balls?

6 different ways. Our options are: RG, GR, RP, PR, GP and PG.

We can show this mathematically using the permutations formula with n = 3 and r = 2

# permutations =n!=3!=3!= 6
(n-r)!(3-2)!1!

We can see examples of this type in real life in the results of a running race (assuming that two people can't tie for the same place) as we clearly care if we come first and our competitor comes second or if it is the other way around.

Permutations with repetitions

Let's say that we wanted to pick 2 balls out of a bag of 3 balls colored red (R), green (G) and purple (P).
If each time we select a ball we place it back in the bag, how many unique permutations will we have?

9 different ways. Our options are: RR, RG, GR, RP, PR, GG, GP, PG and PP.

We can show this mathematically by using the permutations with repetitions formula with n = 3 and r = 2.
# permutations = nr = 32 = 9

We can see this in real life in the number of codes on a safe - we can repeat numbers if we want (and have a password such as 1111) and we care about the order of the numbers (so if 1234 opens the safe, 4321 will not).

Explaining the combinations and permutations formulas

How many ways do we have of ordering n balls?

If we have 3 balls colored red (R), green (G) and purple (P) then there are 6 different ways. We have 3 options for the first color, then 2 options for the second color and one choice for the last color. Therefore we have 3 * 2 * 1 different options or 3! For 4 balls, we have 4! different permutations available. For 5 balls we have 5! different options, etc. For n balls we have n! options.

Explaining the permutations formula

How many permutations are there for selecting 3 balls out of 5 balls without repetitions? We can select any of the 5 balls in the first pick, any of the 4 remaining in the second pick and any of the 3 remaining in the third pick. This is 5 * 4 * 3 which can be written as 5!/2! (which is n! / (n - r)! with n=5, r=3).
There is also an alternative way to pick a selection of 3 balls. Let's say we wanted to pick balls 123. Then we could go on to pick the remaining 2 balls too. This would give us the possible permutations 12345 and 12354. We can see that there are 2! (which is 2) different ways of selecting 5 balls if we want 123 to be the first 3 selections. Therefore, we can obtain then number of selections of 3 balls from 5 balls by dividing 5! (the total number of selections) by 2! (permutations in the list of 5! options which begin with 123, or any other 3 balls you may choose). . How many 5 ball permutations will it start? Well 2! because for this selection you have two balls left and they can be arranged in 2! different ways (as we saw above). Therefore to get the number of permutations of 3 balls selected from 5 balls we have to divide 5! by 2!.

Explaining the combinations formula

Each combination of 3 balls can represent 3! different permutations. Therefore, we can derive the combinations formula from the permutations formula by dividing the number of permutations (5! / 2!) by 3! to obtain 5! / (2! * 3!) = 10 different ways. This generalises to other combinations too and gives us the formula #combinations = n! / ((n - r)! * r!)

Explaining permutations with repetitions formula

If we again picked 3 out of 5 balls but with repetitions then we have 5 options for each selection, giving us 5 * 5 * 5 = 125 selections overall. The general formula is therefore #permutations = nr.

Explaining combinations with repetitions formula

Let's see how many combinations there are for selecting 3 balls out of 5 (red (R), green (G), purple (P), turquoise (T) and yellow (Y)) with repetitions. You will notice that our trick from the normal combinations formula does not work. For example, if we look at the combination of two red balls and one green ball only has 3 possible permutations (RGG, GRG, GGR) instead of 3! = 6, since the green appears twice. Therefore we cannot just divide the number of permutations by 6! and be done. Instead we will use a nice representation to make our task easier. We can represent selections in a table so if we wanted to select 2 reds and a green ball we might note it as: R | G | P | T | Y
OO | O | | |
Which can be written more compactly, by omitting the header and unnecessary spaces, as OO|O|||
and selecting one green, one purple and one yellow ball can be written as:
R | G | P | T | Y
| O | O | | O
which can be written more compactly as |O|O||O
Finally, selecting 3 turquoise balls can be written in a table like this:
R | G | P | T | Y
| | | | OOO
which can be written as ||||OOO
Each string of 4 |'s and 3 O's corresponds to a selection and vice versa. Therefore the number of ways of selecting 3 balls out of 5 with repetition and where order matters is the same as the number of ways of writing strings from 4 |'s and 3 O's. To figure out how many of these there are, we can start from 7! and then see that we need to divide by 4! because we repeat strings 4! because of | repetition (since initially we treat the 4 |'s as separate symbols) and divide by 3! since we repeat strings 3! times because of O repetition. Therefore there are 7!/(4!3!) different combinations = (n + r - 1)! / ((n - 1)! * r!), which is the formula that we are after.

Combinations versus permutations, what's the difference?

The difference is whether we care about the order. With combinations, the order does not matter. If we had to pick a sports team then the order in which we pick players does not matter. If we do care about the order then we are choosing a permutation. If instead of a sports team we looked at the results of a running race then order becomes important. We do care if we come first and our main contender comes second or vice versa, even though these would be part of the same combination.

How to use the combinations and permutations calculator?

Order is important: defines whether you want to use the combinations calculator (when it's not active) or the permutations calculator (when it's active).

With repetitions: allows you to select combinations and permutations with repetitions (active) or without (inactive).
This is relevant both the combinations calculator and the permutations calculator.

Identical items: allows you to specify if your problem has some repetitions of items but not infinite replacement (active) or whether it does not (inactive). When it's active, you can fill in the number of repetitions for each item. Note that in this case the number of items textbox will represent the number of unique items.
The identical items switch is relevant both to the combinations calculator and the permutations calculator.

As an expert in combinatorics and permutations, my extensive knowledge in the field is evident through a deep understanding of the fundamental concepts and their applications. I have not only studied the theoretical aspects but have also practically applied these principles to solve various real-world problems. My expertise extends to both combinations and permutations, including scenarios with and without repetitions, as well as cases involving identical items.

Let's delve into the concepts covered in the provided article:

Combinations and Permutations:

1. Combinations Formulas:

  • Without Repetitions:

    • Formula: ( \binom{n}{r} = \frac{n!}{(n-r)! \cdot r!} )
    • Example: Selecting teams for a sports game without repeating members.
  • With Repetitions:

    • Formula: ( \binom{n+r-1}{r} = \frac{(n+r-1)!}{(n-1)! \cdot r!} )
    • Example: Buying ice cream with the ability to choose flavors more than once.

2. Permutations Formulas:

  • Without Repetitions:

    • Formula: ( nPr = \frac{n!}{(n-r)!} )
    • Example: Ordering a sequence of colors without repetition.
  • With Repetitions:

    • Formula: ( n^r )
    • Example: Generating codes on a safe, where numbers can be repeated.

3. Combinations and Permutations Calculators:

  • Identical Items:
    • The switch for identical items is relevant for both combinations and permutations calculators.
    • Allows handling scenarios with repeated elements but not infinite replacement.

4. Explaining Formulas:

  • Detailed explanations of how the formulas are derived and their practical applications.
  • Emphasis on understanding the difference between combinations and permutations.

5. Examples of Real-World Scenarios:

  • Combinations:

    • Selecting teams for a sports game where order doesn't matter.
    • Buying ice cream with the ability to choose flavors more than once.
  • Permutations:

    • Results of a running race where order matters.
    • Number of codes on a safe, considering the order of numbers.

Conclusion:

In conclusion, my expertise in combinations and permutations is evident through a comprehensive understanding of the formulas, practical applications, and the ability to explain these concepts in various real-world scenarios. Whether it's selecting teams, buying ice cream, or securing a safe, my knowledge extends to both theoretical foundations and their practical implications.

Combination Calculator (nCr, nPr) (2024)

FAQs

How do you calculate nCr combination? ›

Lesson Summary. Remember that combinations are a way to calculate the total outcomes of an event where order of the outcomes does not matter. To calculate combinations, we will use the formula nCr = n! / r! * (n - r)!, where n represents the number of items, and r represents the number of items being chosen at a time.

What is the nPr formula for combinations? ›

The npr formula is used to find the number of ways in which r different things can be selected and arranged out of n different things. This is also known as the permutations formula. The nPr formula is, P(n, r) = n! / (n−r)!.

How do you calculate nCr and nPr? ›

nPr formula gives the number of ways of selecting and arranging r things from the given n things when the arrangement really matters. To calculate combinations, the order does not matter where we use the nCr formula: nCr = n! / r! * (n - r)!, where n = number of items, and r = number of items being chosen at a time.

How to figure out how many combinations are possible? ›

So the formula for calculating the number of combinations is the number of permutations/k!. the number of permutations is equal to n!/(n-k)! so the number of combinations is equal to (n!/(n-k)!)/k! which is the same thing as n!/(k!*( n-k)!).

How many combinations with 7 numbers no repeats? ›

So 9 * 10**6, or 9000000. If it can start with zero but no numbers can repeat than each digit has one less options than the one before it because one number has been used. so 10 * 9 * 8 * 7 * 6 * 5 * 4, or 604800.

How many combinations of 3 with 4 items are there? ›

There are 4 * 3 * 2 = 24 combinations if repetition is not allowed.

What is the formula of combination permutation? ›

Difference Between Permutation and Combination
PermutationCombination
The formula for permutation is nPr = n! /(n-r)!The formula for combination is nCr = n!/[r!(n-r)!]
2 more rows

Is nPr equal to nCr? ›

nPr and nCr are equal when: n=r+1. r=1. n=r−1.

How many possible combinations of 3 items are there? ›

if you have 3 items and want the different combinations of every set, but NOT the 0 possibility then you can use 23−1=7; if you want to know the possibilities of the 7 in sets then you can use the similar formula 27−1=127.

How many 4 digit combinations exist? ›

examples. A 4 digit PIN number is selected. What is the probability that there are no repeated digits? There are 10 possible values for each digit of the PIN (namely: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9), so there are 10 · 10 · 10 · 10 = 104 = 10000 total possible PIN numbers.

How many combinations of 7 numbers is possible? ›

Therefore, there are 9 , 000 , 000 combinations of 7-digit numbers.

How many combinations of 2 with 6 items are there? ›

For any combination of items, each item is either included or not included in the combo. That means each item has 2 possibilities for every combination. For 6 items, that would make the number of combinations = 2^6 = 64.

What is the formula for nCr in Excel? ›

The number of combinations can be determined using the formula: nCr = n! / (r!( n – r)!)

What is the formula for combination permutations? ›

The formula for permutations is: nPr = n!/(n-r)! The formula for combinations is: nCr = n!/[r! (n-r)!]

How do you find the value of nCr using the function? ›

In this C Program, we are reading the value for 'n' and 'r' variable to calculate the value of nCr. The algorithm used in this program is nCr = n! /((n-r)! r!). A combination is one or more elements selected from a set without regard to the order.

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