standard deviation formula

Mr. John gave his students a test in the class. The scores were normally distributed with a mean of 75 and standard deviation of 4. What percent of the students scored between 71 and 79? => 95% or 99.7% or 68% or 34%..

The 95% confidence interval for the mean number of mangoes in a carton is between 48.12 and 51.88. If a random sample of 27 cartons were used to determine this interval, what was the standard deviation? => 2 or 3 or 4 or 5..

The 95% confidence interval for the mean number of sheets of paper in a ream is between 452.76 and 447.24. If the standard deviation is 10 papers, find the size of the random sample that was used to determine this interval. => 5.52 or 50 or 1.41 or 7.09..

Monthly expenditures for a family of four in a city averages $450, with a standard deviation of $65. Assume the monthly expenditures are normally distributed. Find the probability that a family whose expenditure will be less than $294 or greater than $554. => 0.063 or 0.0548 or ..

An organization conducted a test for a group of students, whose scores are normally distributed with mean 70 and standard deviation 3. Find the probability that the score of a particular student is greater than 67. => 0.8413 or 0.1587 or 0.3413 or 0.5000..

The lifetime of certain kinds of electronic devices have a mean of 350 hours and a standard deviation of 20 hours. The distribution is measured to the nearest hour and can be approximated closely to a normal curve. Find the probability that any one of these devices will have a l..

The average price of the suburban station wagon is $20,000 with a standard deviation of $2000. The median price of the suburban station wagon is $18,000. Find the coefficient of skewness and describe the shape. => 0, symmetric or - 3, negatively skewed or + 3, positively skewed ..

When a distribution is bell-shaped, approximately what percentage of data values will fall within 1 standard deviation of the mean? I. 95% II. 99.7% III. 68% => only III or only I or only II or all are correct..

The mean lifetime of a clock is 30 months. If the distribution is normal with a standard deviation of 4 months, then for how many months should a guarantee be made if the manufacturer does not want to exchange more than 5% of the clocks? => 23 months or 24 months or 20 months or..

The average number of calories that a person consumes per day is 2000. Find the probability that a randomly selected person consumes more than 2500 calories per day assuming a standard deviation of 200. => 62% or 0.62 or 0.62% or 38%..