Finding the average age of first cardiac incident

If the age of an initial cardiac incident is normally distributed with a population standard deviation= 12 years, find the average age at which people will experience their first cardiac incident, given that 17% of all initial cardiac incident victims are younger than 50.

I think z =0.5675 = 0.57

We need to find z such that P(Z<z)=0.17. From standard normal table, …

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