The mean life of a battery used in a digital clock is 305 days. The lives of the battery follow normal distribution. The battery was recently modified to last longer. A sample of 20 of the modified batteries had a mean life of 311 days with a standard deviation of 12 days. The level of significance is .05. What would be your critical value or decision point?
A)1.725
B)2.093
C)1.729
d)2.086
Did the modifications increase the life of the battery?