Probabilty Homework Issues

yackel.richard · Feb 3, 2009

A civil engineering construction firm‘s records show that the probability is 0.2 that one of its new bridges will require repair within a year.

a) What is the probability that the tenth bridge it builds will be the second one to require repair within a year?

b) What is the probability that the sixth bridge it builds will be the first one to require repair?

soroban · Feb 3, 2009

Hello, yackel.richard!

I'll try to explain the first one . . .

A civil engineering construction firm‘s records show that the probability is 0.2
that one of its new bridges will require repair within a year.

a) What is the probability that the tenth bridge it builds will be the second one
to require repair within a year?

\(\displaystyle \text{Of the first nine bridges, exactly one needed repair.}\)
. . \(\displaystyle \text{This probability is: }\:{9\choose1}(0.2)(0.8)^8\)

\(\displaystyle \text{Then the tenth bridge needed repair.}\;\text{ This probability is: }\:0.2\)

\(\displaystyle \text{Answer: }\;9(0.2)(0.8)^8 \times 0.2 \;=\;0.060397978\)

b) What is the probability that the sixth bridge it builds will be the first one to require repair?

\(\displaystyle \text{The first five bridges did not need repair: }\

0.8)^5\)

\(\displaystyle \text{Then the sixth bridge needed repair: }\:0.2\)

\(\displaystyle \text{Answer: }\;(0.8)^5(0.2) \;=\;0.065536\)

Deleted member 4993 · Feb 4, 2009

yackel.richard said:
Please Remove

Why do you want to remove your post?

Do you not want anybody else to to learn from your post?
Or, are you hiding the fact that somebodyelse did your work for you?

A civil engineering construction firm‘s records show that the probability is 0.2
that one of its new bridges will require repair within a year.

a) What is the probability that the tenth bridge it builds will be the second one
to require repair within a year?
b) What is the probability that the sixth bridge it builds will be the first one to require repair?

Duplicate post:

http://answers.yahoo.com/question/index ... 608AA6xyM3

Probabilty Homework Issues

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soroban

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