[tex]z = \frac{x - mean}{stdev} \\ \\ z = \frac{50 - 69}{10} = -1.9[/tex]
The general rule is that 68% of all scores are within 1 z-score of the mean.
95% are within 2 z-scores of the mean.
99% are within 3 z-scores of the mean.
1.9 is pretty close to 2, so this means approximately only 5% of all scores are more unusual than this students' score.
