Probability, not that advance but hey!!

Just hoping someone can help me out here with some answer ive done them but not very confident, please can you show your working out too

1) In computing lab there are 52 students doing an exercise that involves web activity. The average web service response time is 5 seconds and each students spends on average 60seconds student each webpage before issuing a new web page request.

i) Calculate system throughput as number of web page requests per second?

ii)Calculate the average number of students studying web pages and average number of students awaiting web service response.

2)

It is observed that of 200 first year computing students

-10 are women

- 40 students following business computing

i) if a student is selected at random what is the probability that the selected student be a woman? be on business computing ?

ii) What is probability that a student selected at random from business computing students be a woman?

iii) What is probability that a women student selected at random be on business computing

3) Four friends A,B,C and D go together to a store. Because they all are going to different departments of the store (and will only be 2 minutes) they agree to meet again outside the main entrance store. In fact it is ten minutes before they are all together again. A,C and C are outside the main entrance after 3, 4 and 5 minutes respectively. D leas the store after right minutes. But by the wrong door and takes further two minutes to fins how friends.

i) Over 4 Friends what is the average time in store?

ii) Over ten minutes what is average number of the friends in the store>?

iii) In the context of flow through system, let me store be the system and the four friends be the objects flowing through a system and calculate the throughput (as friends per min) during 10 mins.