Tuesday
May 21, 2013

# Homework Help: Statistics (Probability)

Posted by Joe on Monday, November 30, 2009 at 7:30pm.

I have a q

• Statistics (Probability) - Joe (SORRY), Monday, November 30, 2009 at 7:36pm

my apollogies

I have a question and was woundering if you could walk me through this one problem.

A string of Chrristmas lights contains 20 lights. the lights are wired in series, so that if any light fails the whole string will go dar. EAch light has proabability 0.02 of failing during a 3-year period. The lights fail independently of each other. What is the probability that the string of lights will remain bright for 3 years?

Ok I know this is an intersection problem which makes use of the follong problem

p(A intersection B) = p(A)p(B|A)

Ok my problem is I do not know which variable is which with the information given and which variable it is asking me to solve for. I belive it is asking me for this right?

p(B|A)

the probabiltiy of the twenty light bulbs under the condition that they survive

and p(A) is point .02 I know that

I also think that the problem could aslo be asking me for this

p(A intersection B)

I don't know which variable it's asking me for and which variable is which...

I know what probability is and how to use this formula I just have problems connecting the information to each problem and then solving fot the unknown...

so i was woundering if you could walk me through this problem and the through process that allows you to say which variable is which in the formula

Thanks!

• Statistics (Probability) - Joe (SORRY), Monday, November 30, 2009 at 7:38pm

like I get the math I just can't translate the English into the math so that way I can do the math i guess

• Statistics (Probability) - bobpursley, Monday, November 30, 2009 at 7:42pm

You want to know the prob of all lights working for three years, right?

Pr(all working)=.98^20=about 2/3 you can work it out exactly.

• Statistics (Probability) - Joe (SORRY), Monday, November 30, 2009 at 7:46pm

yes but why did you raise it to the twentith power?

what formula is this?

• Statistics (Probability) - bobpursley, Monday, November 30, 2009 at 8:00pm

What is .98*.98*.98 twenty times
.98^20

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