n P 4 = 84 n C 2 Now I'm not even sure if the 84 is multiplying by the N choose 2? I don't understand. Ive done all the practice questions my teacher gave me and this came up on the homework and Ive never encountered a question like this. Thanks in advance. Is there a specific order to do questions like this, how would you go about doing this question?
2026-04-07 06:59:33.1775545173
Struggling a bit with Combinatorics Order in which to do this question?
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I take it that you have to solve the equation $${}_nP_4=84\times {}_nC_2$$
It only makes sense as a question if you are multiplying by $84$ that way: ${}_nP_4={}_{84n}C_2$ is impossible.
Use the definitions $${}_nP_r=\frac {n!}{(n-r)!}$$ and $${}_nC_r=\frac {n!}{n!(n-r)!}$$