Question:
If the number of selections of r as well as (n + r) things from 5n different things are equal, then what is the value of r?
If the number of selections of r as well as (n + r) things from 5n different things are equal, then what is the value of r?
Options:
- a) n
- b) 2n
- c) 3n
- d) 4n
- a) n
- b) 2n
- c) 3n
- d) 4n
correct answer : b)
Explanation:
5nCr = 5nCn+r
n + r + r = 5n Þ 2r = 4n Þ r = 2n
5nCr = 5nCn+r
n + r + r = 5n Þ 2r = 4n Þ r = 2n