The size of the left upper chamber of the heart is one measure of cardiovascular health. when the upper left chamber is enlarged, the risk of heart problems is increased. a paper described a study in which the left atrial size was measured for a large number of children age 5 to 15 years. based on this data, the authors concluded that for healthy children, left atrial diameter was approximately normally distributed with a mean of 26.2 mm and a standard deviation of 4.3 mm. (a) approximately what proportion of healthy children have left atrial diameters l