Practice Problems-1
1. 统计学基本概念代写
A set of final examination grades in an introductory statistics course is normally distributed, with a mean of 73 and a standard deviation of 8.
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- What is the probability that a student scored below 91?
- What is the probability that a student scored between 65 and 89.
- The probability is .05 that a student taking the test scores higher than what grade.
2.
Bayley Scales of Infant Development is a standardized measure used in studies with high-risk infants. It has ap-proximately a normal distribution with a mean of 100 and a standard deviation of 16. (a) What percentage of children have an MDI of at least 120? (b) Find the MDI score that is the 90th percentile. (c) Find and interpret the lower quartile, median, and upper quartile.
3. 统计学基本概念代写
The Chapin Social Insight Test evaluates how accurately the subject appraises other people. In the reference population used to develop the test, scores are approximately normally distributed with mean 25 and standard deviation 5. The range of possible scores is 0 to 41
a）What percentage of the population has scores below 20 on the Chapin test?
b）How high a score must you have in order to be in the top quarter of the population in social insight?
4.
You scored 63 on each of two statistics tests and the class means were equal for the two tests (52.0). Calculate your z scores on the two exams, assuming that the standard deviations are 8.5 and 3.6 respectively. On which test did you perform better?
Compute your percentile rank on each of the two statistics exams (You scored 63 on each).
5. 统计学基本概念代写
Dr. Perez wants to form two extreme groups of subjects with respect to the Barrett Impulsivity Scale (BIS) for a psychology study they are conducting. That is, they want to have two specific values for the BIS, so that if someone scores below the lower point, that individual would be in the lowest 25% of scores; or if the individual scores above the higher point, then the score is in the highest 25%. If we assume that BIS is normally distributed with an overall mean of 50 and a standard deviation of 15, what should the two values be?
6.
A population of 2-liter bottles of water is known to have a mean fill weigh of 2.06 liters and a standard deviation of .02 liters. The population is known to be bell-shaped.
Describe the distribution of fill-weights using the empirical rule.
Approximately 68% falls between
Approximately 95% falls between
Approximately 99.7% falls between
Is it very likely that a bottle will contain less than 2 liters of water?
7. 统计学基本概念代写
A department store, on average, has daily sales of $28,372.72. The standard deviation of sales is $2000. On Tuesday, the store sold $34,885.21 worth of goods.
Find Tuesday’s z score.
Was Tuesday an unusually good day?
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