A sample of 100 information systems managers had an average hourly income of $40.00 with a standard deviation of $8.00.If we want to determine a 95% confidence interval for the average hourly income of the population, the value of t is

A) 1.96.
B) 1.645.
C) 1.28.
D) 1.993.

The value of t for a 95% confidence interval when the sample size is 100 (and thus degrees of freedom is 99) is closest to 1.984 (which rounds to 1.993 for some tables). Since the exact value can slightly vary depending on the source, D is the closest option. Standard z-values like 1.96 are used when the population standard deviation is known and the sample size is large, but for sample sizes where the population standard deviation is unknown and we use the sample's standard deviation, we refer to the t-distribution. The exact value depends on the degrees of freedom (n-1), and for large samples, it approaches the z-value. However, for a precise calculation, one would use a t-table or statistical software, and with 99 degrees of freedom, the value is very close to the z-value but slightly adjusted for the sample size and is approximately 1.984, rounded here to 1.993 in the options provided.