1. The size of the left upper chamber of the heart is onemeasure of cardiovascular health. When the upper left chamber isenlarged, the risk of heart problems is increased. The paper “Leftatrial size increases with body mass index in childrenâ€(International Journal of Cardiology [2009]: 1–7) described a studyin which the left atrial size was measured for a large number ofchildren age 5 to 15 years. Based on this data, the authorsconcluded that for healthy children, left atrial diameters wereapproximately normally distributed with a mean of 26.4 mm and astandard deviation of 4.2 mm.
a. About what proportion of healthy children have left atrialdiameters greater than 32 mm?
b. About what proportion of healthy children have left atrialdiameters between 25 mm and 30 mm?
c. Children in the top 10% of left atrial diameters are at riskof heart problems. What is the left atrial diameter value (theoriginal x value) describing the upper 10% of extreme left atrialdiameters? (Hint: What percentile is this, draw a figure).
