Thank you for the opportunity to help you with your question!
In this problem x stands for the mean and SD the standard deviation. With the mean = 72 and SD = 4, the students with pulses between 68 and 76 are all of the students within one standard deviation of the mean. In general, about 68% of the population falls within one standard deviation of the mean, 95% within two standard deviations and 99.7% within three standard deviations.
To answer the question, 68% of 200 is .68 * 200 = 136. So 136 students have pulses in the range of 68 and 76 beats per minute.
Please let me know if you need any clarification. I'm always happy to answer your questions.
Oct 28th, 2015
Did you know? You can earn $20 for every friend you invite to Studypool!