If Mr. Bisby wants to know the average of the grades on a test, what measure of central tendency would he be looking at? (Spelling counts so make sure to spell it correctly)

The distribution of the amount of money spent by students for textbooks in a semester is approximately normal in shape with a mean of $235 and a standard deviation of $20. according to the standard deviation rule, how much did almost all (99.7%) of the students spend on textbooks in a semester?