There are a number of ways to do this. The first cumulative probability value is 0.05. You can use the standard normal distribution table in last month's newsletter to find the value of z corresponding to 0.05 probability. If you look at the table, you will see that z = -1.64 gives a cumulative probability of 0.0505 and a z = -1.65 gives a cumulative probability of 0.0495. So, the value of z that gives a cumulative probability of 0.05 is between -1.65 and -1.64.