Blood samples taken from children up to ten years old in a certain town show that 54% of the 600 tested have blood-type O. Twenty years later, a new set of blood samples from children up to 10 years old finds that 50% of the 1030 tested now have blood-type O. We want to know if between the first and second tests there was a decrease in the proportion of children having blood type O. The test statistic is

z = 1.56.

z = 2.57.

z = 1.56.