數統幾問有關probability distribution

希望大家教下我^^ [[列式要詳細易明,要用返數統用既公式來解答]]~thx
1. On the average,one of ten persons passing a shop in a shoping centre
enters the shop. Find the probability that the first person who enters the
shop after it open in the morning is
(a) the 6th person who pass.
(b) one of the first 10 persons who pass.

**我剩係識計part (a),唔識計part(b),希望大家教我計part (b)^^

(b)的答案: 06513

2. pigs imported are examined to see whether they carry certain disease that
will affect the health of a consumer.From past records, an average of onepig
in a hundred was found to be unhealthy and was destroyed.
Find the probability that 2 lots of 300 pigs each will contain
(a) no unhealthy pigs between them.
(b) 2 unhealthy pigs between them.

答案:(a): 0.0025 (b):0.0446

3. The number of flaws per metre of cloth has the Poisson distribution with mean
0.5. Rolls of the cloth, each 10m long, are inspected one after another.
Find the probability that
(a) the first roll has no flaw,
(b) the 6th roll is the first one which contains one or more flaws,
(c) 2 out of the first 6 rolls inspected contain no flaw.

答案:(a): 0.0067 (b):1.379 x 10^(-11) (c):0.0007