Question

see attachment

Answer 1

2*pi*r + 8*pi = 2*pi*(r+w)
8*pi = 2*pi*w
=> w = 4

Answer 2

The answer is 4 but given that these are SAT problems and that SAT math problems focus more on insight than grinding out the algebra, I have been looking for the gimmick - well, the concept.

Answer 3

What is the missing concept here?

Circumference is 2 * pi * r. The two circles have different radius (delta w) and their circumference also has a delta (give as 8pi). Simply expression and solving is all that is there to it.

Answer 4

You can immediately set 2 pi r = 8 pi once you see that the circumference is dependent upon the difference in radius of the circles.

Answer 5

How is 2*pi*r = 8?

Answer 6

I mean equal to 8*pi