(b) About 16 percent of the students score below 175. Note that 25 is the standard deviation, and that 175 is one of these standard deviation units below the mean. Looking at the table of percentages for the normal distribution you can see that about 16 percent fall below the point of one standard deviation below the mean.

(c) Note that 250 is 50 units above the mean. This is the same as 2 standard deviation units of 25 each (25 times 2 is 50). If you look at the standard deviation table, you see that only about 2 percent of the scores are higher than 2 standard deviations above the mean.