A researcher for the EPA measured the amount of arsenic in the water near a sewage treatment plant. Over 5 days, he took n = 20 measurements (in parts per billion). His sample data is summarized in the ogive graph shown below (you can click on it to make it bigger). Please note that it's not the same ogive as in the previous question. 20 15 10 5 O 30 35 40 45 50 35 60 65 70 75 Arsenic (DDB) How many measurements taken in this time frame were within 55, 60) ppb? ans =