Scores on the SAT form a normal distribution with a mean of µ = 500 with σ = 100. What is the probability that a randomly selected college applicant will have a score greater than 640?
3
z-scores are distributed according to the standard normal distribution. That is, with the parameters: mean 0 and variance 1.
They are said to be Normally distributed.
If the distribution is Gaussian (or Normal) use z-scores. If it is Student's t, then use t-scores.
99.7% of scores fall within -3 and plus 3 standard deviations around the mean in a normal distribution.
To find the proportion of a normal distribution corresponding to z-scores greater than +1.04, you can use the standard normal distribution table or a calculator. The area to the left of z = 1.04 is approximately 0.8508. Therefore, the proportion of the distribution that corresponds to z-scores greater than +1.04 is 1 - 0.8508, which is approximately 0.1492, or 14.92%.
In a normal distribution, approximately 76.4% of the data falls below a z score of 1.04. Therefore, the proportion of the distribution that corresponds to z scores greater than 1.04 is about 23.6%. This can be found using standard normal distribution tables or calculators.
3
z-scores are distributed according to the standard normal distribution. That is, with the parameters: mean 0 and variance 1.
They are said to be Normally distributed.
Between z = -1.16 and z = 1.16 is approx 0.7540 (or 75.40 %). Which means ¾ (0.75 or 75%) of the normal distribution lies between approximately -1.16 and 1.16 standard deviations from the mean.
If the distribution is Gaussian (or Normal) use z-scores. If it is Student's t, then use t-scores.
The IQs of a large enough population can be modeled with a Normal Distribution
You calculate the z-scores and then use published tables.
-1.28
Approx 78.88 % Normal distribution tables give the area under the normal curve between the mean where z = 0 and the given number of standard deviations (z value) to its right; negative z values are to the left of the mean. Looking up z = 1.25 gives 0.3944 (using 4 figure tables). → area between -1.25 and 1.25 is 0.3944 + 0.3944 = 0.7888 → the proportion of the normal distribution between z = -1.25 and z = 1.25 is (approx) 78.88 %
When putting the scores in, you use the normal distribution graph, which is the best start.