probability problem

2015-04-30 5:07 pm

Please help me to solve the problem.

In a company, there are 40 staffs. All of them wear either glasses or lens or both. It is known that 32 staffs wear glasses. 24 wear lens.

(i) A staff is selected from the company. Find the probabilities that a staff wears both glasses and lens.

(ii) 2 staffs are selected one by one randomly with replacement. Find the probabilities that the second staff wears glasses given that the first staff wears only 1 optical instrument, i.e. wear glass only or wear lens only .

回答 (1)

50418129

2015-04-30 7:37 pm

✔ 最佳答案

(i)

no. of wears glasses = 32
no. of wears lens = 24
no. of wears both = 32 + 24 - 40 = 16
no. of wears glasses only = 32 - 16 = 16
no. of wears lens = 24 - 16 = 8
P(wears both) = 16 / 40 = 2 / 5

(ii)

P(2nd wears glasses | 1st wears glasses or lens only)
= P(2nd wears glasses) (since "with replacement")
= 32 / 40
= 4 / 5

參考: knowledge

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