# [SPM Add Math Permutation and Combination] How to solve this question?

4 (a) Given that { }^{n} \mathrm{P}_{r}={ }^{n-2} \mathrm{P}_{r}, express n in terms of r. Diberi { }^{n} \mathrm{P}_{r}={ }^{n-2} \mathrm{P}_{r}, ungkapkan n dalam sebutan r .

{ }^{n} \mathrm{P}_{r}={ }^{n-2} \mathrm{P}_{r}
This is another interesting question, because based on the following equation, there is no way the following relation can be true in a “physical sense”. This is because arranging n objects in r ways can NEVER be equal to arranging (n-2) objects in r ways. I will prove why in the following calculations.

Solution:

Assuming we run the simplifications using the fundamental principles, we found out that n is smaller than r, which cannot be true in a physical sense : Imaging arranging 3 objects in 8 different ways, how can this be true?

Nevertheless, let me know if the answer is different, or if there is a typo.

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Yeahh It can’t be true…now I understand.your answer is also correct Thank you very much