Answer
SHOWN BELOW
Work Step by Step
(a)
The provided expression as follows:
\[H=\frac{7}{10}\left( 220-a \right)\]
Now, put \[a=20\],as the age for a 20-year-old in the provided expression,
\[\begin{align}
& H=\frac{7}{10}\left( 220-20 \right) \\
& H=\frac{7}{10}\left( 200 \right) \\
& H=7\left( 20 \right) \\
& H=140
\end{align}\]
Hence, the lower limit range of heart rate is 140 beats per minute.
The lower limit of the heart rate range is 140 beats per minute for the age of 20 years old to improve cardiovascular condition.
(b)
The provided expression as follows:
\[H=\frac{4}{5}\left( 220-a \right)\]
Now, put \[a=20\], as the age in provided expression,
\[\begin{align}
& H=\frac{4}{5}\left( 220-20 \right) \\
& H=\frac{4}{5}\left( 200 \right) \\
& H=4\left( 40 \right) \\
& H=160 \\
\end{align}\]
Hence, the upper limit of range is 160 beats per minute.
The upper limit of the heart rate range is 160 beats per minute for the age of 20 years old to improve cardiovascular condition.
