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

The answer is:

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

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:

`(h)/(0.8)=(0.8( 220-x ))/(0.8)\\\Rightarrow (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}`