# 急做statistical probability..20

(a) Hong Kong Government is promoting the use of energy efficient home appliances, including light bulbs. According to results of a concern group, the life-time of a particular brand of energy saving light bulb is found to be normally-distributed with mean life time of 5864 hours and standard deviation of 328 hours.

(i) Find the value of t hours such that 95% of such light bulbs can last longer than t hours. (5 marks)

(b) The production of energy saving light bulbs requires quality control process. Each light bulb is inspected before being shipped to the market. On average, 10% of such light bulbs produced are defective and 10% of such light bulbs are misclassified in the quality control process.

(i) Present the above information with a tree diagram. (3 marks)

### 1 個解答

• 7 年前
最愛解答

Please read:

2013-12-11 19:25:06 補充：

表的左方加上表的上方的數是quantile

-(1.60 + 0.04) = -1.64

睇 -1.64 對應表中的 .0505 代表 standard normal -1.64 以左的 area/proportion/probability 是 5.05%

睇 -1.65 對應表中的 .0495 代表 standard normal -1.65 以左的 area/proportion/probability 是 4.95%

2013-12-11 19:25:17 補充：

如果問那個quantile可使standard normal 以左的 area/proportion/probability 是 5% (即以右的是 95% ), 那從上述資料可以推出是 -1.645

你看:

以左　　　　　以右

-1.64　　　5.05%　　94.95%

-1.65　　　4.95%　　95.05%

所以

-1.645　 5%　　 95%