standard_description: Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used.
problem_activity: Task
Suppose $P$ is a point not contained on a line $L$.
Let $Q$ be the point on $L$ so that $PQ$ meets $L$ perpendicularly and let
$R$ be any other point on $L$ as in the picture below:
[IMG]
Show that segment $PQ$ is shorter than segment $PR$.


aligns: no