In a certain presidential election, 38% of voting-age Americans actually voted. In our town of 200,000, 40% of voting-age citizens voted. What are the z-score and standard deviation? (Round the z-score to one decimal place and the standard deviation to four decimal places.)

This is how I had done it: the Median is 100,000, the Mean is 100,000 as well. So I had done: (80,000-100,000)/20,000=-1 but I got it wrong. Can you help me please