STT 231 EXAM 2 CERTIFICATION
EVALUATION TEST 2026 FULL QUESTIONS
AND CORRECT ANSWERS GRADED A+
●● normal density curve.
Answer: symmetric about the mean μ; has standard deviation σ; total
area under the curve = 1.0; values of the random variable X on x-axis;
probabilities are represented by areas under the curve;
●● what do the numbers in the N(0,1) equation represent?.
Answer: the first number is the mean (mu), and the second is the SD
(sigma)
●● what is the equation for a standard normal curve/distribution, and
what do the axes represent?.
Answer: N(0,1) the x axis represents z-scores, and the y is the
probability
●● what is the domain for a standard normal curve? which particular
interval are we interested in?.
Answer: the actual domain=infinite, but we are interested mostly in (mu
+/- 3sigma)
, ●● difference between pnorm and qnorm commands.
Answer: pnorm: gives proportion/percent of data within the given range
qnorm: gives the cutoff range for the percentile of data inputted
●● what are the required arguments for pnorm? qnorm?.
Answer: pnorm(upper cutoff, mean, SD)
qnorm(upper percentile cutoff, mean, SD)
●● when do you use the lower.tail=false argument?.
Answer: during p/qnorm commands, when you are interested in the right
side distribution
●● normal model for sampling distribution of pi hat.
Answer: still follows the rule of standard normal curve (N(0,1)), but it
uses N(pi, SE equation) because
●● what is standard error? how do you interpret the results?.
Answer: it measures how close the current sample data reflects the
overall population predicted data, a high standard error value represents
that your sample is not very reflective of the population and is very
spread out, vice versa for low
●● how do SE and sample size n relate?.
EVALUATION TEST 2026 FULL QUESTIONS
AND CORRECT ANSWERS GRADED A+
●● normal density curve.
Answer: symmetric about the mean μ; has standard deviation σ; total
area under the curve = 1.0; values of the random variable X on x-axis;
probabilities are represented by areas under the curve;
●● what do the numbers in the N(0,1) equation represent?.
Answer: the first number is the mean (mu), and the second is the SD
(sigma)
●● what is the equation for a standard normal curve/distribution, and
what do the axes represent?.
Answer: N(0,1) the x axis represents z-scores, and the y is the
probability
●● what is the domain for a standard normal curve? which particular
interval are we interested in?.
Answer: the actual domain=infinite, but we are interested mostly in (mu
+/- 3sigma)
, ●● difference between pnorm and qnorm commands.
Answer: pnorm: gives proportion/percent of data within the given range
qnorm: gives the cutoff range for the percentile of data inputted
●● what are the required arguments for pnorm? qnorm?.
Answer: pnorm(upper cutoff, mean, SD)
qnorm(upper percentile cutoff, mean, SD)
●● when do you use the lower.tail=false argument?.
Answer: during p/qnorm commands, when you are interested in the right
side distribution
●● normal model for sampling distribution of pi hat.
Answer: still follows the rule of standard normal curve (N(0,1)), but it
uses N(pi, SE equation) because
●● what is standard error? how do you interpret the results?.
Answer: it measures how close the current sample data reflects the
overall population predicted data, a high standard error value represents
that your sample is not very reflective of the population and is very
spread out, vice versa for low
●● how do SE and sample size n relate?.
