The document presents a statistical question regarding the boiling temperature of a substance, which follows a normal distribution with a mean of 120 and a standard deviation of 20. It asks for the probability of the temperature being greater than 130, less than 150, and between 120 and 140. The document is focused on probability calculations based on the normal distribution of the boiling point.

1. 7. The temperature at which a certain substance boils is normally distributed with a mean of 120
and a standard deviation of 20 . What is the probability that the temperature at which a certain
sample of this substance is
(a) bigger than 130 ?
(b) smaller than 150 ?
(c) between 120 and 140 ?