Question

One way to calculate the target heart rate of a physically fit adult during exercise is given by the formula h=0.8( 220−x ), where h is the number of heartbeats per minute and x is the age of the person in years. Which formula is equivalent and gives the age of the person in terms of the number of heartbeats per minute?

Answer 1

Answer:

The answer is:

C. $\bold{x = -1.25h+220}$

Step-by-step explanation:

Given:

$h=0.8( 220-x )$

Where $h$ is the heartbeats per minute and

$x$ is the age of person

To find:

Age of person in terms of heartbeats per minute = ?

To choose form the options:

$A.\ x=176-h\\B.\ x=176-0.8h\\C.\ x=-1.25h+220\\D.\ x=h-0.8220$

Solution:

First of all, let us have a look at the given equation:

$h=0.8( 220-x )$

It is value of $h$ in terms of $x$.

We have to find the value of $x$ in terms of $h$.

Let us divide the equation by 0.8 on both sides:

$\dfrac{h}{0.8}=\dfrac{0.8( 220-x )}{0.8}\\\Rightarrow \dfrac{1}{0.8}h=220-x\\\Rightarrow 1.25h=220-x$

Now, subtracting 220 from both sides:

$\Rightarrow 1.25h-220=220-x-220\\\Rightarrow 1.25h-220=-x$

Now, multiplying with -1 on both sides:

$-1.25h+220=x\\OR\\\bold{x = -1.25h+220}$

So, the answer is:

C. $\bold{x = -1.25h+220}$