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prabability..

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prabability..

by warlock » Wed Aug 06, 2008 3:26 am
It's 6:00 P.M., and Amy has to stay in the office until her sister Isabel calls her. After each full hour that Amy is in the office, there is a 70% chance Isabel will call her. What is the probability that Isabel calls her at 9:00 P.M., and no sooner?

a)0.027
b)0.063
c)0.09
d)0.147
e)0.343
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by parallel_chase » Wed Aug 06, 2008 3:44 am
Probability that isabell will call amy per hour is 70/100

There are 3 hours between 6-9 PM

Probability that Isabel will not call her between 6-7 = 30/100
Probability that Isabel will not call her between 7-8 = 30/100
Probability that Isabel will call her between 9-10 = 70/100

Total probability is 30/100*30/100*70/100 = 0.063

Hence B is the answer.

Whats the OA?
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by warlock » Wed Aug 06, 2008 3:55 am
OA = B

thank you..
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