9 . E
To be symmetric about the origin means that, for any point A on the graph, there is another
point B on the graph such that the origin is the midpoint of AB. So you should be able to
start at any point on the graph, draw a straight line segment to the origin, continue straight
the same distance beyond the origin, and be at another point on the graph. Thus, for
example, you can see that (A) does not work:
But (E) does work:
10 . C
George has 5 choices for the first book and then 4 choices for the second. That’s 20
permutations for taking 2 books out of 5. But this is a combinations question. Order doesn’t
matter. Whether he reads A or B first, it’s the same combination of 2 books, so you have to
divide the 20 permutations by 2. If you like formulas, here’s how to do this one:
