Usually the best thing to do to start on a plane geometry question is to mark up the figure. Put as
much of the information into the figure as you can. Doing so is a good way to organize your
thoughts and avoid having to go back and forth between the figure and the question.
Now you can plan your attack. First subtract from the whole length to get :
= − = (3a + 15) − (7a + 5) = 3a + 15 − 7a − 5 = −4a + 10
MARK UP THE FIGURE
Try to put all the given information into the figure so that you can see everything at a glance
and don’t have to keep going back and forth between the question stem and the figure.
Then, because Y is the midpoint of , you can divide by 2 to get and :
Watch out! That matches choice (B), but is not the final answer. What you’re looking for is , so
you have to add:
= + = (7a + 5) + (−2a + 5) = 5a + 10
The answer is (E).