There are five independent stages in the repair of a certain piece of computer equipment.The repair time for each stage is exponentially distributed with average value of 10minutes.What is the probability that a customer engineer can repair the equipment in an hour or less?Not more that 90 minutes?

Question

king · Answer

5/9??

anonymous · Answer

Can you tell me how did u get that ?

king · Answer

Is it rite?

anonymous · Answer

Ive got a diff answer, ...which method did u use?

king · Answer

what answer u got and by which method?I got 2 answers by using 2 diff. methods..

anonymous · Answer

As it said "exponentially distributed" , i've used the exponential distribution 
$$1-e ^{-\lambda x}$$

anonymous · Answer

So how did u solve it?

king · Answer

i used the exponential distribution method for 1 answer and for the other i used the normall probability method by finding out sample space,no.of jobs etc....

anonymous · Answer

Hmmm...but i guess its only the expo. dist. that we need to use...the 1st bit askes us to find P{X<=60} and 2nd one P{X<90}

anonymous · Answer

For F(x)=$$1-e ^{-\lambda x}$$ , where i got lambda=0.1 ( from given avg=10)

king · Answer

0.10?

king · Answer

1/10?

anonymous · Answer

yeah, since in expo. dist. mean=1/$$\lambda$$ 
given mean=10 (avg=mean) and hence $$\lambda$$ =1/10=0.1

anonymous · Answer

Okay, so what was ur answer?? for 1st bit i've got the answer as 0.99752 , which is the prob that a stage can be reapired, but the question asks "complete equipment" and that s where i got stuck...

anonymous · Answer

*repaired

king · Answer

4.287...but i shall check with my sir and let u know....

anonymous · Answer

How is it? did u do this:
P{X<=60}= 1- e$$^{-(0.1)(60)}$$ = 0.99752 

can you plz type how have you got 4.28?? coz if u know, probability always lies between 0 and 1

king · Answer

i know that's why i wanted to ask my sir...

anonymous · Answer

Okay....but u need the answer today...gotta submit tomorrow

anonymous · Answer

*I need it