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الدرس : التباديل
Permutations of less than all
We have seen that the number of ways of choosing 2 letters from 4 is 4· 3 = 12. We call this
"The number of permutations of 4 different things taken 2 at a time."
We will symbolize this as 4P2:
4P2 = 4· 3
The lower index 2 indicates the number of factors. The upper index 4 indicates the first factor.
For example, 8P3 means "the number of permutations of 8 different things taken 3 at a time." And
8P3 = 8· 7· 6
= 56· 6
= 50· 6 + 6· 6
= 336
For, there are 8 ways to choose the first, 7 ways to choose the second, and 6 ways to choose the third.
In general,
nPk = n(n − 1)(n − 2)· · · to k factors
Permutations Calculator
An online calculator to calculate the number of permutations of n elements taken r a the time.
n P r = n! / (n-r)!
How to use the calculator
1 - Enter the positive integers n and r and press " Compute n P r ".
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رياضة 2 التباديل آلة حاسبة للتباديل أون لاين