Many electronic devices use disposable batteries, which eventually have to be replaced. Assume that for one particular brand and type of battery, the distribution of the hours of useful power can be approximated well by a Normal model. The mean is 140 hours, and the standard deviation is 4 hours.
% Using the 68 - 95 - 99.7 Rule, sketch the appropriate model.
-b. The marketing department wants to write a guarantee for battery life. What lifespan should they quote so that they can expect 98% of the batteries to meet the guarantee?
-& The company's research department has been given the task of improving the batteries, with a goal that at least 90% of the new batteries should last longer than the average of the current type. Initial research suggests that a mean of 143 hours is attainable. What other-improvement must they make to achieve their goal?
