For each of the following variables, determine the level of measurement.

(a) Gender

(b) Temperature

(c) Number of days during the past week that a college student studied

(d) Letter grade earned in your statistics class

Approach 

For each variable, we ask the following: Does the variable simply categorize each individual? If so, the variable is nominal. Does the variable categorize and allow ranking of each value of the variable? If so, the variable is ordinal. Do differences in values of the variable have meaning, but a value of zero does not mean the absence of the quantity? If so, the variable is interval. Do ratios of values of the variable have meaning and there is a natural zero starting point? If so, the variable is ratio.