Question
If $\frac{{ }^{n} P_{r}}{120}=\frac{{ }^{n} C_{r}}{5}$, then $r$ is(a) 4(b) 5(c) 24(d) 600
Step 1
We know that ${ }^{n} P_{r} = \frac{n!}{(n-r)!}$ and ${ }^{n} C_{r} = \frac{n!}{r!(n-r)!}$. Show more…
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