Question

1. In recent years, SAT scores are approximately normal with a mean of 1100 and a SD of 130, while ACT scores are also approximately normal with a mean of 22 and a SD of 6.5. Without any studying, you took both tests and scored 1250 on the SAT and 24 on the ACT.

a) Did you do better on the SAT or the ACT? Make sure to find the percentile (what percent of the test takers scored lower than you?) of each score and compare.

b) You know you can do better, so you plan to spend the entire summer preparing to retake the SAT, and you’re aiming to score in the 97th percentile. What score will put you in the 97th percentile? For full credit, show all your work.

c) What proportion of the students would score between 1250 to 1400 on the SAT?

2. The American Medical Association (AMA) wishes to determine the proportion of doctors who are considering leaving the profession because of the rapidly increasing number of lawsuits against doctors. How large a sample should be taken to find the answer within a margin of error of ±3% at the 96% confidence level? Use an estimate of ?=̂ 0.5 in your calculation.

Answer 1

SAT

= 1100

= 130

X = 1250

Z = 1.15

ACT

= 22

= 6.5

X = 24

Z = 0.31

a) Did you do better on the SAT or the ACT? Make sure to find the percentile (what percent of the test takers scored lower than you?) of each score and compare.

As Z score for SAT is more than ACT , hence, students did better in SAT

b) You know you can do better, so you plan to spend the entire summer preparing to retake the SAT, and you’re aiming to score in the 97th percentile. What score will put you in the 97th percentile? For full credit, show all your work.

For 97th percentile

P[ X < x ] = 97% = 0.97

P[ Z < 1.88 ] = 0.97

x - 1100 = 1.88*130

x - 1100 = 244.4

x = 1100 + 244.4

x = 1344.4

P[ X < 1344.4 ] = 97% = 0.97

c) What proportion of the students would score between 1250 to 1400 on the SAT?

We need to compute . The corresponding z-values needed to be computed are:

Therefore, we get: