According to a recent poll, 26% of adults in a certain area have high levels of cholesterol. they report that such elevated levels "could be financially devastating to the regions healthcare system" and are a major concern to health insurance providers. according to recent studies, cholesterol levels in healthy adults from the area average about 207 mg/dl, with a standard deviation of about 20 mg/dl, and are roughly normally distributed. if the cholesterol levels of a sample of 50 healthy adults from the region is taken, answer parts (a) through (d). what is the standard deviation?