Question

According to medical data, the ages at which patients have their first knee replacement surgery

follows a normal distribution. The average age for a first knee replacement is 58 years of age, with a
standard deviation of 8.25 years. Therefore, doctors can expect the middle 68% of their knee
replacement surgery patients to be between what ages?

Answer 1

The doctors can expect the middle 68 % of their knee replacement surgery patients to be between 49.75 years and 66.25 years.

Explanation:

68 % of the knee replacement surgery patients implies that the ages lies within x = x₀ ± σ where x₀ = mean age = 58 years and σ = standard deviation = 8.25 years

So, the ages lies between x₀ + σ and x₀ - σ

So, the ages lie between 58 - 8.25 = 49.75 years

and 58 + 8.25 = 66.25 years

So the doctors can expect the middle 68 % of their knee replacement surgery patients to be between 49.75 years and 66.25 years.