Percentages + standard deviation - practice problems
Number of problems found: 20
- IQ scores
IQ scores are normally distributed with a mean of 100 and a standard deviation of 15. What percentage of the population scores higher than 125 on an IQ test? - Suppose 12
Suppose in a physics test involving 30 students, and four scored 75%, eight scored 60%, twelve scored 50%, and six scored 30%. Calculate the mean of the group and the standard deviation. - A random
A random sample of 225 nails in a manufacturing company is gathered. The engineer specified that the specified length of a nail must be 8 cm having a standard deviation of 0.04 cm. It shows from the sample that the average length of the nails is 8.055 cm. - Suppose 8
Suppose the scores on a test have a normal distribution with X=74 and a standard deviation of s=18. What percentage of students have scores higher than 90? What percentage of students have scores between 70 and 85? Twenty percent of the students do better
- Normally distributed
Suppose the height of male youngsters is normally distributed with a mean of 60 inches and a standard deviation of 10. what percentage of the boy's height would we expect to be between 44 and 75, less than 49, and 76 and more? - Quartile statistics
Use the following data, which was obtained from a study of weights of adult men, to answer problems: Mean ; 192 lb ; First quartile ; 178lb Median; 185lb ; Third quartile ; 232 lb Mode ; 180 lb ; 86th percentile ; 239 lb Standard Deviation ; 23lb; ; a) Wh - Z score transformation
The annual salary of an entry-level statistics major (in thousands of dollars) is normally distributed with a mean of 75 and a standard deviation of 12. X ∼ N ( μ = 75, σ = 12 ). What is the minimum salary a statistics major should aim for in order to ear - Two sigma
Khail took his math test and scored 88. If the class average was 78 with a standard deviation of 5, what percent of students earned a higher grade than Khail's grade? - The number 5
The number of hours per week the television is turned on is determined for each family in a sample. The mean of the data is 35 hours, and the median is 31.2 hours. Twenty-four families in the sample turned on the television for 20 hours or less for the we
- Distribution 67074
The time required to complete the test has a normal distribution with a mean of 50 minutes and a standard deviation of 10 minutes. What percentage of students take the test within 30 minutes? - 68-95-99.7 rule
Assume the resting pulse rates for a sample of individuals are normally distributed with a mean of 70 and a standard deviation of 15. Use the 68-95-99.7 rule to find the following quantities. a. Percentage of pulse rates less than 70 b. percentage of puls - Significance 61784
Determine the interval estimate of the standard deviation of the meantime to find a parking space. We found out from a survey of 200 residents that the average time is one hour and 25 minutes, and the standard deviation is 15 minutes. Use a 1% significanc - Germination 55283
The supplier of spruce seeds for our nursery declares a germination rate of 80% for his goods. Verify this statement based on an experiment in which only 70 seeds germinated out of 100 randomly selected seeds. - Suppose 4
Suppose that 14% of all steel shafts produced by a certain process are nonconforming but can be reworked (rather than having to be scrapped). Consider a random sample of 200 shafts, and let X denote the number among these that are nonconforming and can be
- Unemployment rate
Over the last 16 years, the country's unemployment rate has changed according to the following frequency table: years of unemployment: 2 5 2 3 3 1 unemployment rate: 0.5 1 1.5 2 2.5 3 in % (percent). Determine the two-sided confidence interval for the var - Three sigma rule
The height of trees in a given stand is known to be a quantity with a normal probability distribution with a mean value of 15 m and a variance of 5 m². Determine the interval in which there will be tree heights in such a stand with a probability of 90% - Complaints
The table is given: days; complaints 0-4; 2 5-9; 4 10-14; 8 15-19; 6 20-24; 4 25-29; 3 30-34; 3 1.1 What percentage of complaints were resolved within two weeks? 1.2 calculate the mean number of days to resolve these complaints. 1.3 calculate the modal nu - Statistician 7500
A statistician monitored the variance of monthly wages and found its value to be 640,000. Determine the standard deviation of salaries if there is a one-off increase: a) about CZK 1,800, b) about 5%. - Grade point average
The average GPA is 2.78, with a standard deviation of 0.45. If GPA is normally distributed, what percentage of the students have the following GPAs? Solve for the z-score and report the appropriate percentage: a. Less than 2.30 b. Less than 2.00 c. More t
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