If the standard deviation in Prob. 5 were smaller, would

If the standard deviation in Prob. 5 were smaller, would that percentage be larger or smaller?

Data from Prob. 5

If the lifetime X of a certain kind of automobile battery is normally distributed with a mean of 5 years and a standard deviation of 1 year, and the manufacturer wishes to guarantee the battery for 4 years, what percentage of the batteries will he have to replace under the guarantee?