Aresearcher (jack) comes to you and is interested in the average length of time a computer fan will run before it needs to be cleaned. jack believes that this time period is approximately normally distributed with a standard deviation of 30 hours. you tell him to take a sample of computer fans. jack comes back to you and says that he took a random sample of 36 computers, and found that the average length of time was 876 hours. use a 94% confidence interval.

94% confidence interval for the average length of time a computer fan will run before it needs to be cleaned is between 866.6  and 885.4 hours

Step-by-step explanation:

94% confidence interval can be calculated using M±ME where

margin of error (ME) around the mean using the formula

ME= where

Using the numbers we get ME= =9.4

Then the 94% confidence interval is 876±9.4

mr. flanders’ class sold 47 doughnuts and   mr. rodriquez’s class sold 38 cartons of milk

step-by-step explanation:

let x be the number of doughnuts sold by mr. flanders’ class and y be the number of cartons sold by mr. rodriquez’s class.

1. together, the classes sold 85 items, then

x+y=85.

2. both classes earn earned $104.49 for their school. if doughnuts were sold for $1.35 each, then x doughnuts costed $1.35x. if cartons of milk were sold for $1.08 each, then y cartons costed $1.08y. hence,

1.35x+1.08y=104.49.

3. solve the system of two equations: