Aperson who is 15 years old had a target heart rate range of

I believe it would be your resting pulse rate subtracted from 205.So, Figure out your pulse rate by counting how many beats for 10 seconds, then multiply it by 6. Subtract that amount from 205. Example : Pulse rate - Beats 10 times in 10 seconds. Multiply 10 x 6 = 60. 205-60 = 145 

Between 70 and 100 bpm

The person who utilize the progression principle will keep adding the difficulty of the exercise that he's doing, while the person who does not, will only stay stagnant.  the person that utilize progression principle, will get a stronger endurance because now his body is conditioned to do harsher routines.{the answer was already on verified)