Question

If nP_r = 720(nC_r), then r is equal to:

Options

• 4

• 5

• 6

• 7

Answer 1

6

Explanation:

Given nP_r = 720(nC_r)

`(n!)/((n-r)!) = 720 (n!)/(r!(n-r)!)`

1 = `720/(r!)`

r! = 720

r! = 6 × 5 × 4 × 3 × 2 × 1

r! = 6!

r = 6