Normal heart rate The normal resting heart rate for adults is 60 to 100 beats per minute. The heartbeat rate in a sample of 400 patients was tested. It was found that the distribution of the number of beats per minute is roughly normally distributed with an average of 80 and a standard deviation of 12 .

a. Find the proportion of individuals in the sample whose heartbeat rate is in the normal range.

b. Tachycardia refers to any heartbeat rate greater than 100 beats per minute. Estimate the number of individuals in the sample who could have tachycardia.