I think it should be

P(C) = ((n-k) over r) (1/5)^r * (1 - 1/5)^(n-k-r)

E[C]=((n-k) over r) (1/5)^r * (1 - 1/5)^(n-k-r)*1

Alumni Liaison

Ph.D. 2007, working on developing cool imaging technologies for digital cameras, camera phones, and video surveillance cameras.

Buyue Zhang