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S1 Probability help

Hi,

I've been trying to do this question and I've done the first part but I'm stuck on the second one.

"Xavier, Yuri and Zara attend a sports centre for their judo club's practice sessions. The probabilities of them arriving late are, independently, 0.3, 0.4, 0.2 respectivelty.

Calculate the probability that for a particular practice sessions:

a) all three arrive late => (0.3x0.4x0.2) = 0.024
b) none of the three arrives late => (0.7x0.6x0.8) = 0.336
c) only Zara arrives late => (0.3x0.4x0.2)+(same bracket again)+(same bracket again) = 0.072

b) Zara's friend, Wei also attends the club's practice sessions. The probability that Wei arrives late is 0.9 when Zara arrives late and is 0.25 when Zara does not arrive late.

Is it basically saying that the probability that Wei arrives late given that Wei arrives late too is 0.9 and 0.25 given that Zara does not arrive late?

so P(W|Z) and P(W|1-Z)?

questions are: give the probability that:

2a) Both Zara and Wei arrive late
2b) Either Zara or Wei, but not both arrive late.

Also if there are 1654 employees out of which there are 710 males out of which 38 work in managerial sector, 369 in academic, 303 in support and three employees are selected at random without replacement, what is the probability that:

3a) all three employees are male/ I got 0.0789 (710/1654)*(709/1653)*(708/1652)
3b) exactly one employee is male/ I got 0.245 ((1-(710/1654))

Could anyone help me and explain how to do this with as many scenarios as possible? Possibly with the answers as I'm hopeless at just reading how to do something without seeing it or the answer or working out. Please read my answers carefully as I'm quite sure they're quite wrong.