Expected Value

[匿名]

2011-02-26 2:08 am

An air-conditioner normally requires 4 servicing in 10 years on the average. First servicing is free of charge, subsequently the charge is $150 per visit. The air-conditioner will be returned to factory if servicing exceeds 6 times in 10 years. What is the expected servicing charge of the air-conditioner in 10 years?

更新1:

Answer is $423.

更新2:

To: 自由自在 Sorry that your answer cannot be seen on imageshack because I am not registered, please post the answer on yahoo, thanks.

更新3:

To : 自由自在. Please explain why the last term is P(X ≥ 6) x 5 and not P(X = 6) x 5? My understanding is that when X > 6, the air-conditioner is already returned to factory, why is there a servicing charge?

更新4:

T0 : 自由自在. Thanks for your explanation. But in examination, you don't know the answer in advance, so how to decide it is P(X = 6) x 5 or P(X ≥ 6) x 5?

回答 (1)

用戶9112

2011-02-27 3:54 am

✔ 最佳答案

Do you have a numeric answer?

2011-02-26 19:54:02 補充：
http://img204.imageshack.us/img204/8752/23462178.png

圖片參考：http://img204.imageshack.us/img204/8752/23462178.png

2011-02-26 23:21:03 補充：
see here:
http://i1090.photobucket.com/albums/i376/Nelson_Yu/9.jpg

2011-02-27 09:33:14 補充：
when you call for the service at the 6th time, you do not know there will be a 7th time. So by the time you do the 6th service, you already paid 5 times. when you call for the 7th time, the air conditioner will be returned, but there should be no refund.

2011-02-27 09:33:17 補充：
This is the reason why I asked fo rthe numeric answer to make sure I understand the question.

2011-02-27 12:09:56 補充：
It is then up to the examiner to make sure they set a question without ambiuity. It is not the probelm for a student to guess correctly what the examiner wants to mean. By the ways, always use common sense.

2011-02-27 12:10:01 補充：
You have to call for the service and pay. Only when the quota is exceeded, the machine is returned. Before this is done, you already paid for the 5 services.

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