Question 647251
An IQ score of 154 is two standard deviations above the mean. [112 + 2(21) = 154]

95% of the population is within 2 standard deviations of the mean. That means that  2.5% of the population is lower than 2 standard deviations below the mean and 2.5% is above 2 standard deviations above the mean. Therefore 2.5% have IQ greater than 154 (and 2.5% have IQ below 70 because it is 2 standard deviation below the mean).