When to use the formula (nCr x nCr)/nCr?

In summary, the formula for calculating combinations is nCr = n! / (r! * (n-r)!), where n is the total number of items and r is the number of items selected at a time. A combination is different from a permutation in that the order does not matter in a combination, whereas it does in a permutation. Combinations are used in probability when the order of selection does not affect the outcome, and they cannot be used with replacement. To solve a real-world problem using combinations, identify the total number of items and the number of items to be selected, then use the combination formula to find the total number of possible combinations. This can be useful in scenarios such as choosing a password or predicting lottery numbers.
  • #1
jasper10
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Homework Statement



I was wondering for what situations one uses the formula:
(nCr x nCr)/ nCr ?
Thanks

Homework Equations



nCr
 
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  • #2
jasper10 said:
I was wondering for what situations one uses the formula:
(nCr x nCr)/ nCr ?
You mean (nCr x nCr)/ nCr = nCr? ;)

There's a reason you use different letters to represent different quantities. It's hard to answer your question when you have removed all that information from the formula.
 
  • #3
well i mean for example,

5C2 x 4C3 / nCr
 

FAQ: When to use the formula (nCr x nCr)/nCr?

What is the formula for calculating combinations?

The formula for calculating combinations is nCr = n! / (r! * (n-r)!), where n is the total number of items and r is the number of items selected at a time.

How is a combination different from a permutation?

A combination is a selection of items where the order does not matter, while a permutation is a selection of items where the order does matter.

How do you know when to use combinations in probability?

Combinations are used in probability when the order of selection does not affect the outcome, such as selecting a committee or a group of winners.

Can combinations be used with replacement?

No, combinations cannot be used with replacement. Combinations involve selecting items without replacement, meaning that once an item is selected, it cannot be selected again.

How do you use combinations to solve a real-world problem?

To use combinations to solve a real-world problem, first identify the total number of items and the number of items to be selected. Then, plug those values into the combination formula to find the total number of possible combinations. This can be useful in scenarios such as choosing a password or predicting lottery numbers.

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