Question 238634
To achieve the maximum benefit for the heart when exercising, your heart rate 
(in beats per minute) should be in the target heart rate zone.
 The lower limit of this zone is found by taking 70% of the difference between 220 and your age. The upper limit is found by using 85%.
:
D) Two women in an aerobics class stop to take their pulse, and are surprised to find that they have the same pulse. 
One woman is 36 years older than the other and is working at the upper limit of her target heart rate zone.
The younger woman is working at the lower limit of her target heart rate zone.
 What are the ages of the two women, and what is their pulse?
:
Let x = age of the younger
then
(x+36) = age of the older
:
The younger pulse equation (lower limit)
P = .70(220-x)
:
The older pulse equation (upper limit)
P = .85(220-(x+36))
P = .85(220 - 36 - x)
P = .85(184-x)
:
Young pulse = Old pulse
.70(220-x) = .85(184-x)
154 - .70x = 256.4 - .85x
-.70x + .85x = 256.4 - 154
.15x = 2.4
x = {{{2.4/.15}}}
x = 16 yrs old is the young one
then
16 + 36 = 52 yrs is the oldie
:
:
Prove this by finding the pulse of each
.85(220-52) = 142.8
.70(220-16) = 142.8