Question
If ^ 22 P_ r+1 : ^ 20 P_ r+2 =11: 52, then r is equal to
BITSAT
Mathematics
Permutation Combination
2024
BITSAT 2024 (Memory Based Paper 2)
BITSAT Mathematics Question (2024) — Solution
Options
- A. 3
- B. 5
- C. 7
- D. 9
Answer
C. 7
Step-by-step solution
^ 22 P_ r+1 : ^ 20 P_ r+2 =11: 52 or (21-r)(20-r)(19-r)=52 2 21 (21-r)(20-r)(19-r)=14 13 12 aligned & (21-r)(20-r)(19-r)=(21-7)(20-7)(19 \\ & -7) aligned r=7
Related: Mathematics — Permutation Combination · All PYQ Banks