Question

3. If nP5 + 5x 9P4 = 10Pr, find r.​

Answer 1

Answer:

r = 5

Step-by-step explanation:

9p5 + 5* 9p4 = 10pr

9! / 4! + 5 x 9! / 5! = 10!/ (10-r)!

cancelling the 9! on LHS and 10! on RHS

1/4! + 5/5! = 10/ (10-r)!

taking LCM

5+5/ 5! = 10 / (10-r)!

5! = (10-r)!

=> 5 = 10-r

r = 5