GIVEN
The study claims that 85% of students are procrastinators. From a random sample of 169 students, 133 identify as procrastinators. The level of significance is 0.05.
SOLUTION
The test statistic (z-score) can be calculated using the formula:

where

From the question, the following parameters can be seen:

Substitute known values into the formula:

Therefore, the test statistic is -2.29.