A. 21
B. 18
C. 3
D. 20
If nPr =30240 and nCr=252then the ordered pair (n, r) is equal to
The sum of all possible numbers greater than 2000 formed by using the digits 2,3,4,5 is
The number of four digited numbers that can be formed from using the digits 2,4,5, 7,8 that are divisible by 4 is
A student is allowed to select atmost n books from a collection of (2n+1) books. If the total number of ways in which he can select books is 63, then n=