5 Screws are sold in packets of 15. Faulty screws occur randomly. A large number of packets are tested for faulty screws and the mean number of faulty screws per packet is found to be 1.2 .
- Show that the variance of the number of faulty screws in a packet is 1.104 .
- Find the probability that a packet contains at most 2 faulty screws.
Damien buys 8 packets of screws at random.
- Find the probability that there are exactly 7 packets in which there is at least 1 faulty screw.