standard deviation formula

If the probability of a defective bolt is 0.05, then find the mean and the standard deviation for the distribution of defective bolts in a total of 400. => 19, 2 0 or 20, 1 9 or 19, 20 or 20, 2 0..

A standard notebook is supposed to have on an average, 200 pages, with a standard deviation of 2 pages. From a supply of 2500 notebooks, a random sample of 40 notebooks was taken and found that the mean number of pages in the notebook was 197. Determine the standa..

The mean score on a standardized test is 100 with a standard deviation of 8. A random sample of 48 scores was found to have a mean of 98. Test at the 0.05 level of confidence and state whether or not to accept the null hypothesis. => The null hypothesis is accepted or ..

The local authorities in a certain city install 1600 electric lamps in the streets of the city. If the lamps have a mean life rate of 1000 burning hours, with a standard deviations of 150 hours, find the value of - 2 standards deviations form the mean. Assume..

The average monthly insurance premium paid by 15 managers is $90 with a standard deviation of $5. 31 officers pay an average of $65 with the standard deviation of $8.63. At 90% confidence, find the test value. Do the managers pay less average premium than the..

The university authorities wanted to estimate the average age of the students in their university by taking a random sample of 25 students. The standard deviation was found to be 3 years. Find the 95% confidence interval for the variance (σ 2 ) and standard ..

Assume that the weights of 3,000 students at a university are normally distributed with mean 150 pounds and a standard deviation of 7 pounds. If 100 samples of 30 students each are obtained, then what would be the expected mean and standard deviation of the r..

The distances traveled in kilometers by a person on four different days is: 63, 42, 55, 40. Find the mean distance and standard deviation. => Mean = 54, standard deviation = 9.5 or Mean = 54, standard deviation = 6.3 or Mean = 50, sta..

The probability distribution for the number of clients visiting a bookshop daily is presented as under. Find the mean and the standard deviation of the distribution. What is the expected number of clients visiting the bookshop? => mean = 67.66, standard deviationh..

60% of the people in a community are eligible to vote. If 100 people are selected at random, then find the standard deviation of the number of people who are eligible to vote. => 24 or 4.89 or 60 or 40..