Simplify: \(^{n}C_{r} ÷ ^{n}C_{r-1}\)
FURTHER MATHEMATICS
WAEC 2015
Simplify: \(^{n}C_{r} ÷ ^{n}C_{r-1}\)
- A. \(\frac{n(n-r)}{r}\)
- B. \(\frac{n}{r(n-r)}\)
- C. \(\frac{1}{r(n-r)}\)
- D. \(\frac{n+1-r}{r}\)
Correct Answer: D. \(\frac{n+1-r}{r}\)
Explanation
\(^{n}C_{r} = \frac{n!}{(n-r)! r!}\)
\(^{n}C_{r - 1} = \frac{n!}{(n - (r - 1))! (r - 1)!}\)
\(^{n}C_{r} ÷ ^{n}C_{r - 1} = \frac{n!}{(n - r)! r!} ÷ \frac{n!}{(n-(r-1))!(r-1)!}\)
= \(\frac{n!}{(n-r)! r!} \times \frac{(n-(r-1)! (r-1)!}{n!}\)
= \(\frac{(n + 1 - r)! (r - 1)!}{(n - r)! r!}\)
= \(\frac{(n+1-r)(n-r)! (r-1)!}{(n-r)! r (r - 1)!}\)
= \(\frac{n + 1 - r}{r}\)
Post an Explanation Or Report an Error
If you see any wrong question or answer, please leave a comment below and we'll take a look. If you doubt why the selected answer is correct or need additional more details? Please drop a comment or Contact us directly. Your email address will not be published. Required fields are marked *