Mary is 14 years old. her resting heart rate 70 beats per minute. calculate 50% of mary maximum heart rate to fine her target heart rate

The maximum heart rate (MHR) is the rate at which the human heart of a given person reaches the highest demands. At rest, the heart rate is about 60 to 80 beats per minute.

Ther's two ways to calculate the maximum heart rate, the most used method is:
MHR = 220 - age 
So, for Mary: MHR = 220 - 14 = 206 beats per minute (bpm)

The second method:
MHR (2) = 217 - (0.85 *age)
For Mary:
MHR (2) = 217 - (0.85 *14) = 205 beats per minute (bpm)

We can conclude that the two methods give approximately the same result, but it can differ if we compare them with an elderly person.

Now we can calculate Mary's target heart rate:
Target heart rate = MHR * 50% = 206 * 0.5 = 103 beats per minute (bpm)

Mary's target heart rate is 103 beats per minute (bpm).

True. the more you know, the better of you will be.