Question

9. Susan has a homework assignment due every thurs- day. She also has a pet dog named Box. Early each thursday morning, Box eats her homework with probability 0.15. In eleven weeks, what is the probability that at least two, but not all, of her homeworks are eaten? Assume that Box acts inde- pendently from week to week!

Answer 1

n=11 , p = 0.15

P ( X = 0) = C (11,0) * 0.15^0 * ( 1 - 0.15)^11=		0.1673
P ( X = 1) = C (11,1) * 0.15^1 * ( 1 - 0.15)^10=		0.3248

P ( X = 11) = C (11,11) * 0.15^11 * ( 1 - 0.15)^0=   0.0000

P(2≤x≤10) = 1 - P(x=0) - P(X=1) -P(X=11) = 0.5078 (answer)