Question
If ${ }^{20} C_{r}={ }^{20} C_{2 r+5}$, then find the value of $r$.
Step 1
We know that ${ }^{n} C_{r}={ }^{n} C_{n-r}$, so we can rewrite the given equation as ${ }^{20} C_{20-r}={ }^{20} C_{2 r+5}$. Show more…
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