Construct a 95% con dence interval for the di erence between the mean lifetimes oftwo kinds of light bulbs, given that a random sample of 100 light bulbs of the rst kindlasted on the average 400 hours of continuous use and 100 light bulbs of the second kindlasted on the average 420 hours of continuous use. The population standard deviations areknown to be1

An automated water dispenser fills packets with one liter of water on average, with a standard deviation of 5 milliliter. the manual says that after a year of operation the dispenser should be tested to see if it needs recalibration. a year later a number of filled packets are set aside and measured separately. it is found that the average packet now contains about 0.995 liters. does the dispenser need calibration? explain your answer.

Which inequality comparing two of the expressions is true when 0.7 < x < 0.9

If, while training for a marathon, you ran 60 miles in 2/3 months, how many miles did you run each month? (assume you ran the same amount each month) write your answer as a whole number, proper fraction, or mixed number in simplest form. you ran __ miles each month.