P(Z<-1.29) is the normal distribution p-value corresponding to a Z-score of -1.29. P(Z<-1.29) tells us the cumulative probability, which is the area to the left of the given Z-score. Because the distribution is symmetrical about the mean, we can use tables to find P(Z<1.29)=0.9015 approx. This is the area (probability) to the left of this Z-score. The area to the right of Z=1.29 is the same size as the area to the left of Z=-1.29 because of symmetry. The total area under the normal distribution is 1 (sum of all probabilities), so the area to the right of Z=1.29 is 1-0.9015=0.0985. Therefore P(Z<-1.29)=0.0985. This is often quoted as a probability percent=9.85%.