Today, Americans’ scores on the Wechsler IQ test are normally distributed with mean 100 points and standard deviation 15 points. However, the typical IQ of Americans has been increasing about 3 points per decade.
a. Estimate the typical IQ (by today’s standards) of Americans two decades ago.
b. Substitute appropriate values for all but one of the variables in the formula z = x –  /s and then solve the equation to find the z-score for the IQ you found in part (a)
c. Substitute appropriate values for all but one of the variables in the formula x = x + zs and then solve the equation to find the z-score for the IQ you found in part (a). Compare the result with the z-score you found in part (b)