The 68 - 95 - 99.7 rule (empirical rule) states that 68% of the population lies within one standard deviation of the mean, 95% of the population lies within two standard deviations and 95% of the population lies within three standard deviations.
Hence since it was said that within 1 deviation (of the mean) of all people like MATH 123, therefore the number of people that like MATH 123 is:
number of people that like MATH 123 = 68% of the population
number of people that like MATH 123 = 0.68 * 1000
number of people that like MATH 123 = 680 students
