Question

Scores on the Wechsler Adult Intelligence Scale (WAIS) are approximately Normal with mean 105 and standard deviation 16. People with WAIS scores below 73 are considered intellectually disabled when, for example, applying for Social Security disability benefits. According to the 68-95-99.7 rule, about what percent of adults are intellectually disabled by this criterion

Answer 1

Answer:

2.5% of adults are intellectually disabled by this criterion

Step-by-step explanation:

The Empirical Rule(68-95-99.7 rule) states that, for a normally distributed random variable:

68% of the measures are within 1 standard deviation of the mean.

95% of the measures are within 2 standard deviation of the mean.

99.7% of the measures are within 3 standard deviations of the mean.

In this problem, we have that:

Mean = 105

Standard deviation = 16

The normal distribution is symmetric, which means that 50% of the measures are below the mean and 50% are above.

What percent of adults are intellectually disabled by this criterion

Below 73

73 = 105 - 2*16

So 73 is 2 standard deviations below the mean.

Of the 50% of the measures that are below the mean, 95% are within 2 standard deviations of the mean, that is, between 73 and 105. The other 100 - 95% = 5% are below 73. So

0.05*0.5 = 0.025

0.025*100 = 2.5%

2.5% of adults are intellectually disabled by this criterion