standard deviation formula

The average price of a computer is $750. If prices of computers are approximately normally distributed with a standard deviation of $75, then what is the probability that a randomly selected computer costs more than $1000? => 3.3% or 0.33% or 0.04% or 0.4%..

The scores made by candidates in a certain test are normally distributed with mean 500 and standard deviation 100. What is the percentage of candidates who scored less than 400? => 15.87% or 17.85% or 18.57% or 15.78%..

The scores made by candidates in a certain test are normally distributed with mean 500 and standard deviation 100. What percentage of candidates received scores which differ from 500 by more than 150 points? => 43.23% or 13.36% or 43.32% or 6.68%..

55% of the students passed in an online examination. If 600 students are selected at random, then find the variance and standard deviation of the number of students passing the examination. => 148.5, 12.19 or 330, 12.19 or 330, 148.5 or 12.19, 148.5..

A machine produces bolts, of which 10% are defective. Find the probability that in a random sample of 400 bolts produced by the machine, 55 or more will be defective. Assume a standard deviation of 6. => 0.970 or 0.0079 or 0.079 or 0.0097..

If two samples have means of 24 and 28 and standard deviations of 4 and 6, with 12 and 15 as the sizes, find the z score for difference of two population means. => 2.07 or 7.73 or 1.07 or 1.93..

In a random sample of 25 trees, the variance in height was found to be 6.9. Find the 95% confidence interval for the standard deviation. Assume that the variable is normally distributed. => between 4.9 and 13.7 or between 4.2 and 13.4 or between 5.5 and 14.1 or between 5.5 and 1..

Which of the following statement(s) is/are false? I. The coefficient of nondetermination is found by subtracting the coefficient of determination from 1. II. As the correlation coefficient approaches zero, the coefficient of determination increases more rapidly. III. The standard error of..

The shoe sizes of 10 students in a class are 4, 3, 5, 6, 3, 6, 5, 4, 3, 6. Find the variance ad standard deviation of the data. σ => Variance = 1.45; Standard deviation = 1.1 or Variance = 1.45; Standard deviation = 1.2 or Variance =..

40% of the people in a town X used the library last year. If 750 people are selected at random, then what is the standard deviation of the number of people who used the library last year? => 13.4 or 180 or 300 or 134..