Standard normal probabilities without a computer
Questions about normal distributions can be answered in terms of areas under a standard normal probability density. These areas might be obtained very roughly by eye from a graph, but a computer should be used to evaluate the area more accurately. For example, most spreadsheets contain functions to evaluate standard normal probabilities.
Similar calculations can be done without a computer. Most introductory statistics textbooks contain printed tables with left-tail probabilities for the standard normal distribution.
These tables can be used after the required probability has been translated into a problem relating to the standard normal distribution.
Note that...