John, who is training with margaret, has no heart monitor, and he cannot afford to buy one. he has to rely on his watch and his ability to measure his own pulse on his wrist. john is 27 years old and wants to train at the higher end of aerobic range, between 75% and 85% of his maximal heart rate. on his last run, john counted 30 heart beats in 15 seconds. is he training within his target range?