22. Five mark example problem V

A mobile phone is put to use when the battery power is \(100 \%\).The percent of battery power '\(y\)' remaining after using the mobile phone for \(x\) hours is assumed as \(y = -0.25x + 1\).

 

(i) Draw the graph of the equation.

 

(ii) Find the number of hours elapsed if the battery power is \(40 \%\).  hours.

 

(iii) How much time does it take so that the battery has no power?  hours.