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Assume life expectancy varies normally. If average life expectancy to reach 90, and 10% of people...

Assume life expectancy varies normally. If average life expectancy to reach 90, and 10% of people live to be 102.8 or longer, what would the standard deviation have to be?

Question 7 options:

7

10

12

5
math   Statistics-And-Probability   
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Answer #1

P(X > 102.8) = 0.1

P(Z > z) = 0.1

z = 1.28

Z = (X - mean)/sd

1.28= (102.8 - 90)/sd

1.28= 12.8 /sd

sd = 10

option B) is correct

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