Question

if number of permutations of n objects taken r at a time without repetition is 720 and number of combination taken r at a time is 120 find value of r​

Answer 1

Answer:

r = 3

Step-by-step explanation:

If number of permutations of n objects taken r at a time without repetition is 720 and number of combination taken r at a time is 120 find value of r​

ⁿPr  = 720

ⁿCr = 120

ⁿPr = n!/(n-r)! = 720

ⁿCr = n!/(r!)(n-r)! =120

ⁿPr/ⁿCr = (n!/(n-r)! )/( n!/(r!)(n-r)!)  = 720/120

=> r! = 6

=> r! = 3 * 2 * 1

=> r! = 3!

=> r = 3