(a).

Sayra kept track of amount time in minutes that she studied the night before an exam

and the percentage that she earned on the exam.

From the table of data the following regression garph is obtained.

Observe the graph :

The quadratic equation obtained from the graph is .

(b).

The quadratic equation is .

Differentiate with respect to .

Amount of time spent by sayra to achieve the score is calculated by equating .

Therefore sayra spent nearly to achieve the score.

Maximum test score earned by sayra is calculated by sunstiuting the amount of time spent

by sayra in the quadratic equation .

Therefore sayra maximum test score is .

(c).

Observe the graph :

From the table and the obtained graph the percentage decreases even though the amount

of time increases.

Therefore more time spent studying does not necessarily result in a higher exam score.

(a). 

(b).

Sayra maximum test score is , to achieve this sayra spent  to achieve this score.

(c).

The percentage decreases even though the amount of time increases.