Juan wanted to investigate how exercise affects heart rate. a classmate sat quietly for 5 minutes before juan used a stopwatch to count her pulse for 15 seconds. a second classmate ran in place for 5 minutes before juan used the stopwatch to find his pulse rate for 15 seconds. after both measurements, juan multiplied the number by 4 to determine hear rate per minute. what did juan do wrong in this investigation? what should juan have done instead?