Ashley P.

asked • 10/14/19

Probability - Binomial Distribution

It has been found that 80% of all printers used operate correctly at the time of installation. A seller sells 10 units during a month.

1)find the prob.that at least 9 of the printers operate correctly at the time of installation.

2)Consider 5 months in which 10 units are sold per month. What is the prob.that at least 9 units operate correctly in each of the 5 months

For 1st part :

Let p(o)=probability that a given printers operates correctly

So we have to find p(o>=9) here.

I understand that for the first part we have use Binomial distribution

But how do we solve the 2nd part?

1 Expert Answer


Ashley P.

Thanks a lot for the response! For part b, why do we simply multiply that values 5 times? Is there any theorem/law etc. behind that?


Kevin B.

Yes, it is the Multiplication Rule for Independent Events. Another example of that would be rolling a dice and getting a six. The probability of rolling the number one is 1/6. But if you want to find the probability of rolling two "ones" in a row then you multiply 1/6 by 1/6 = 1/36. Likewise, the probability of three "ones" would be (1/6)(1/6)(1/6). The events are independent since the vs roll has no impact on the other rolls. I hope that helps.


Ashley P.

Thanks a lot for the clearer explanation!


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