18(2) + 18

*b*= 45

36 + 18

*b*= 45

18

*b*= 9

*b*= 0.5

Note that since the diagram is drawn to scale, you can actually eyeball it and verify the answer you got with the math. It looks to me like 4

*b*'s can fit into each arc marked 2, so 0.5 makes sense for

*b*.

Set up a ratio now using [part]/[whole] = [part]/[whole]*.

[part of the circumference] = 0.5

[whole circumference] = 45

[degree measure of our arc] =

*x*°

[degree measure of whole circle] = 360°

0.5/45 =

*x*°/360°

180° = 45

*x*° (cross multiply)

*x*° = 4°

The answer is (A), 4°.

We can verify this with everything else we know, just to make sure. Because we figured out before that 4

*b*'s go into one of the bigger arcs, we know the bigger arcs must be 16°. There are 18 of each size arc. 18x16° = 288°, and 18x4° = 72°. 72°+288° = 360°. Done.

*

*TONS*of circle questions on the SAT can be solved using this ratio, which can take the general form:

or, more usefully: