Standard deviation - practice problems - page 5 of 6
The standard deviation, symbol sigma σ, is a statistical measure of the variability of a data set. Simply put, it tells us how spread out the values are around the mean (arithmetic mean). How far away most of them are from the mean. It is a non-negative number, defined as the square root of the variance of the data. It therefore has the same dimensions as the data.Variance in statistics is the average of the squares of the deviations from the mean (mean). Variance is also a non-negative number.
The sample standard deviation is defined as the square root of the sample variance. When calculating the sample variance, for n data, only (n-1) independent data are considered.
Number of problems found: 114
- Tallest people a
As a group, the Dutch are amongst the tallest people in the world. The average Dutchman is 184 cm tall. If a normal distribution is appropriate, and the standard deviation for Dutchmen is about 8 cm, what is the percentage of Dutchmen who will be over 2 m - The raw
The raw data presented here are the scores (out of 100 marks) of a market survey regarding the acceptability of a new product launched by a company for a random sample of 50 respondents: 40 45 41 45 45 30 30 8 48 25 26 9 23 24 26 29 8 40 41 42 39 35 18 25 - Corresponding 33321 The following data on the height and the corresponding number of pupils were found in the measurement of 63 pupils: the height; number of pupils 159cm; 1 161cm; 1 162cm; 2 163cm; 1 164cm; 2 165cm; 2 166cm; 3 167cm; 2 168cm; 4 169cm; 3 170cm; 5 171cm; 6 17
- Statistical XY file
Year; money spent on advertising; profit (three values each row) 2008 2 12 2009 5 20 2010 7 25 2011 11 26 2012 15 40 1. draw a scatter diagram depicting the data. 2. calculate the Pearson's correlation coefficient. 3. determine the linear regression equat
- Marketing Year; money spent on advertising; profit 2008 2 12 2009 5 20 2010 7 25 2011 11 26 2012 15 40 1. draw a scatter diagram depicting the data. 2. calculate the Pearson's correlation coefficient. 3. determine the linear regression equation.
- 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
- Tennis aces
The number of aces served by Novak Djokovic in the last 20 tournaments he has participated in is shown below. 12 17 13 7 8 14 11 14 10 12 15 9 11 13 6 15 18 5 19 24 1.1 using the raw, determine the range. 1.2 Group the data into a frequency distribution w - IQ Intelligence quotient Intelligence quotient (IQ) is a standardized score used as the output of standardized intelligence psychological tests to quantify a person's intelligence with the rest of the population (respectively, to a given group). Intelligence has an approximately
- Assembly time
The assembly time for the toy follows a normal distribution with a mean of 75 minutes and a standard deviation of 9 minutes. The company closes at 5 pm every day. If one starts assembling at 4 pm, what is the probability that he will finish before the com
- Alopecia
Medical literature indicates that 45% of men suffer from alopecia. For a random sample of 8 men, calculate the probability that: (a) exactly four men suffer from alopecia. (b) at most, two men suffer from alopecia. - Stoaches Stoaches are fictional creatures distantly related to bigfoot and yeti. Stoach weights are normally distributed, with a mean of 904g and a standard deviation of 104g. State the probability that the sample mean of a random sample of 36 stoach weights excee
- Variability 29933
In September, students missed the following number of lessons: Girls: 2; 0; 7; 8; 2; 2; 4; Boys: 4; 4; 0; 3; 10; 3; 8; Compare the variability of both statistical files. - Distribution 29371 Let the random variable ξ represent the number of satisfied customers. The probability of a satisfied customer for each of the four customers is 7/10. Specify: a) probability distribution, distribution function F(x) and P(-0.5 < ξ < 3.1) b) variance
- Lifespan
The lifetime of a light bulb is a random variable with a normal distribution of x = 300 hours, σ = 35 hours. a) What is the probability that a randomly selected light bulb will have a lifespan of more than 320 hours? b) To what value of L hours can the la
- Average height
There are twice as many girls in the class as there are boys. The average height of girls is 177 cm, and boys 186 cm. What is the average height of students in this class? - Ball bearings One bearing is selected from the shipment of ball bearings. It is known from previous deliveries that the inner bearing radius can be considered a normal N distribution (µ = 0.400, σ2 = 25.10^−6). Calculate the probability that the selected radius will ex
- Life expectancy
The life expectancy of batteries has a normal distribution with a mean of 350 minutes and a standard deviation of 10 minutes. What is the range in minutes 68% of the batteries will last? What is the range in minutes? How long will approximately 99.7% of b - 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%. - Standard deviation
Find the standard deviation for the dataset (grouped data): Age (years); No. Of Persons 0-10 ; 15 10-20 ; 15 20-30 ; 23 30-40 ; 22 40-50 ; 25 50-60 ; 10 60-70 ; 5 70-80 ; 10
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