Question

Assume that the readings at freezing on a batch of thermometers are normally distributed with a mean of 0°C and a standard deviation of 1.00°C. A single thermometer is randomly selected and tested. Find P67, the 67-percentile. This is the temperature reading separating the bottom 67% from the top 33%.

P67 =
°C

Answer 1

Explanation:

To find the temperature corresponding to the 67th percentile, we need to find the z-score that has an area of 0.67 to the left of it in the standard normal distribution. We can use a table or a calculator to find this z-score.

Using a standard normal distribution table, we can look up the value that corresponds to an area of 0.67 to the left of the mean, which is 0.44. This means that P(Z ≤ 0.44) = 0.67, where Z is the standard normal random variable.

Next, we can use the formula for standardizing a normal random variable to convert this z-score to the corresponding temperature on the thermometer scale:

z = (x - μ) / σ

where μ is the mean, σ is the standard deviation, and x is the temperature we want to find.

Rearranging this formula, we get:

x = μ + z * σ

Plugging in the values, we get:

x = 0 + 0.44 * 1.00

x = 0.44

Therefore, the temperature corresponding to the 67th percentile is 0.44°C.