Question

if ¹²P_r = 1320 then r is
1. 1
2. 2
3. 3
4. 4

Answer 1

Correct Answer - Option 3 : 3

Concept:

ⁿP_r = \(\rm n!\over(n-r)!\)

Calculation:

¹²P_r = 1320

\(\rm 12!\over(12-r)!\)= 1320

\(\rm 12!\over(12-r)!\)= 12 × 11 × 10

\(\rm 12!\over(12-r)!\)= 12 × 11 × 10 × \(\rm 9!\over9!\)

\(\rm 12!\over(12-r)!\)= \(\rm 12!\over9!\)

\(\rm 12!\over(12-r)!\)= \(\rm 12!\over(12-3)!\)

∴ r = 3