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Question

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.

Answer 1

If 20% of dogs are older than 22.8 years, then 22.8 must be the 80%ile.

The z-score for 80% is z=0.85

To solve for the standard deviation, (22.8-19.4) / (standard deviation) = 0.85

Solve for standard deviation.

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