To find out what \((r \cdot s)(a)\) represents, we need to combine the two functions \(r(a)\) and \(s(a)\) and analyze what they mean.
- \(r(a) = 211 - 0.64a\) represents the heart rate in beats per minute for a person of age \(a\) years.
- \(s(a) = 525,600a\) represents the lifespan in minutes of a person who is \(a\) years old (since there are 525,600 minutes in a year, this function essentially calculates the total number of minutes a person lives based on their age in years).
When we multiply \(r(a)\) and \(s(a)\): \[ (r \cdot s)(a) = r(a) \cdot s(a) = (211 - 0.64a) \cdot (525,600a) \] This expression gives us the total number of heartbeats a person has in their lifetime, based on their age \(a\) (in years).
So, the correct interpretation of \((r \cdot s)(a)\) is: the total number of heartbeats in a lifetime of a person who is \(a\) years old.