confidence intervals

A manufacturer of incandescent bulbs claims that the average life time of a bulb is 1,000 hours with a standard deviation of 1.6 hours. The inspection department selected a random sample of 42 incandescent bulbs and found their average life time as 998.50 hours. At α = 0.1, can the claim be r..

A cigarette manufacturer claims that the nicotine content of its cigarette is 1.05 mg. A sample of 20 cigarettes were selected and found that the mean nicotine content is 1.40 mg with a standard deviation of 0.77 mg. At α = 0.05, is there enough evidence to reject the manufactutrer's claim? A..

A manual of Medical Information reports that the average weight of a new born baby is 7 pounds. As per the data collected from 14 maternity hospitals, the average weight of a newborn was 7.1 pounds with a standard deviation of 0.2 pounds. Is there enough evidence to reject the report at α = 0..

To predict the outcome of a referendum an opinion poll is conducted. A random sample of 678 people on the electoral roll are asked, " Will you vote for A ? " Their answers are recorded as either "Yes" or "No". If 333 people say "Yes", then find a 95% confidence interval for the ..

A food technologist wishes to estimate the effects of chicken's diet on the cholestrol content of the yolks of the resulting eggs. She has selected a random of 350 eggs from chickens, which were given the standard diet and found that the cholestrol content in the yolks of 280 eggs to be 10.53 mg/g ..

A chocolate manufacturing company reported that milk chocolate bars of 1.5 to 1.6 ounce have 230 calories on an average. A researcher selected a sample of 100 chocolate bars and found the average as 229.6 calories and a standard deviation of 2.3 calories. Is there enough evidence to reject the manu..

A manufacturer claims that the new nickel - metal hydride battery used in mobile phones has a talking time of 300 minutes before recharging. A researcher selected 45 samples with new battery and found that the mean talking time is 294.4 minutes with a standard deviation of 15.03 minutes. Is there e..

The lengths (in miles) of 10 rivers taken randomly are shown here. Find the 98% confidence interval for the variance and standard deviation. Assume that the variable is normally distributed. 1928 1728 1234 1110 1000 2340 1995 2005 1947 1857 => 82215 < σ 2 < 853095 ; ..

A random sample of the assets (in millions of dollars) of 10 families of a colony is shown. Find the 80% confidence interval for the variance of the assets. Assume that the variable is normally distributed. 0.5 1 0.4 1.3 0.8 1.2 0.9 2 0.7 1.5 => between 0.158 and 0.529 or betwee..

The life expectancy (years) at birth of a random sample of 20 countries is shown here. Find the 99% confidence interval for the standard deviation. Assume that the variable is normally distributed. 77 67 76 69 60 57 59 55 57 53 54 50 51 49 50 49 72 69 50 48 => between 6.65 and 1..