Asked Jan 14, 2020

How do you know when to use nPr​ and when to use nCr​ ​ in Permutations and Combinations problems? Please show some examples to make this point clear.


Expert Answer

Step 1

Generally, Permutation used when we have to arrange the objects and Combination is used when we have to select the from the objects.

Step 2

Consider the example, Sachin, Nitin and Amit are three friends and can sit on three benches.

Because, here we have to find out the arrangement. So, we use the Permutation for this problem.

The possible arrangement could be –

Algebra homework question answer, step 2, image 1
Step 3

The same problem could be...

Algebra homework question answer, step 3, image 1

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Permutations and Combinations