2. Many electronic devices use disposable batteries, which event ally 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.

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?
c) The company's research department has been given the tax
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?

d) Explain what the improvement you suggest in partc would
mean about the new batteries.