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.

Question

 A single thermometer is randomly selected and tested. Find P81, the 81-percentile. This is the temperature reading separating the bottom 81% from the top 19%.

Answer 1

To start this, we need to begin this with the z-score corresponding to the 81^st percentile. It corresponds to z=0.88. Then, we have that 0.88= x-μ/σ, or if we substitute:

0.88 = (x-0)/1

Then, solve for x = 0.88 degrees Celsius.