A random sample of 100 households was selected as part of a study on electricity usage, and the number of kilowatt-hours (kWh) was recorded for each household .The average usage was found to be 10.5 kWh. In a very large study in the previous year it was found that the standard deviation of the usage was 3.2 kWh. Assuming the standard deviation is unchanged ond + bet the diotrib uted

On the planet of Mercury, 4-year-olds average 2.8 hours a day unsupervised. Most of the unsupervised children live in rural areas, considered safe. Suppose that the standard deviation is 1.3 hours and the amount of time spent alone is normally distributed. We randomly survey one Mercurian 4-year-old living in a rural area. We are interested in the amount of time X the child spends alone per day.

The warranty on a car battery is 30 months. If the breakdown times of this battery are normally distributed with a mean of 40 months and a standard deviation of 8 ​months, determine the percent of batteries that can be expected to require repair or replacement under warranty.    what ​% of batteries can be expected to require repair or replacement under warranty.​ (Round to two decimal places as​ needed.)

On the planet of Mercury, 4-year-olds average 3.1 hours a day unsupervised. Most of the unsupervised children live in rural areas, considered safe. Suppose that the standard deviation is 1.3 hours and the amount of time spent alone is normally distributed. We randomly survey one Mercurian 4-year-old living in a rural area. We are interested in the amount of time X the child spends alone per day. (Source: San Jose Mercury News) Round all answers to 4 decimal places where possible. b.  Find the probability that the child spends less than 3.3 hours per day unsupervised. c.  What percent of the children spend over 5.1 hours per day unsupervised. % (Round to 2 decimal places)d.  77% of all children spend at least how many hours per day unsupervised?  hours.

claim the standard deviation of pulse rates in adult women is at least 50. for a random sample of adult females the pulse rates have a standard deviation of 11.6.

In a school district, all sixth grade students take the same standardized test. The superintendant of the school district takes a random sample of 3030 scores from all of the students who took the test. She sees that the mean score is 169169 with a standard deviation of 7.06747.0674. The superintendant wants to know if the standard deviation has changed this year. Previously, the population standard deviation was 1313. Is there evidence that the standard deviation of test scores has decreased at the α=0.005α=0.005 level? Assume the population is normally distributed. Step 1 of 5:  State the null and alternative hypotheses. Round to four decimal places when necessary. Step 2 of 5:  Determine the critical value(s) of the test statistic. If the test is two-tailed, separate the values with a comma. Round your answer to three decimal places.     Step 3 of 5:  Determine the value of the test statistic. Round your answer to three decimal places. Step 4 of 5:  Make the…