The average age of a breed of dog is 19.4 years. If the distribution of their ages is normal and 20% of dogs are older than 22.8 years, find the standard deviation.
Answers
Given : The average age of a breed of dog is 19.4 years. If the distribution of their ages is normal and 20% of dogs are older than 22.8 years
To find : the standard deviation.
Solution:
The average age of a breed of dog is 19.4 years
=> Mean = 19.4
distribution of their ages is normal
20% of dogs are older than 22.8 years
=> 80 % Dogs are of lesser age than 22.8 Years
Z score for 80 % is 0.842
Value = 22.8
Z score = ( value - Mean)/.SD
=> 0.842 = ( 22.8 - 19.4)/SD
=> SD = 3.4/0.842
=> SD ≈ 4
standard deviation = 4
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