Answer
$K(3) − K(2)>K(8) − K(7)$
$K$ concave downward.
Work Step by Step
Most students learn more in the third hour of studying than in the eighth hour, so $K(3) − K(2)$ is larger than $K(8) − K(7)$.
In other words, as you begin studying for a test, the rate of knowledge gain is large and then starts to taper off, so $K'(t)$
decreases and the graph of $K$ is concave downward.
