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**kid funky fried** Currently we are learning gamma,exp, uniform, and normal distributions.

I am having trouble with the following homework problem:

The time to failure of a personal computer display tube is exponentially distributed with mean three years.

a) A company offers insurance on these tubes for the first year of usage. On what percentage of policies will they have to pay a claim?

I think for this I should do

1-e^(-1/3)=.2835

b) If an user order three such display tubes (two tubes as spare), what is the

probability that he need to order such tube within six years?

Here is what I did for this:

3*mean of 3 = 9

So,

e^(-x/9)

P{x<6}= 1-e^(-6/9)= .4866

Am I on the right track???

Any help is greatly appreciated.