Radius of larger circle = R
Radius of smaller circle = r

2.Pi.(R-r) = ?

St1

Pi(R^2) - Pi(r^2) = 4

Pi[R^2 - r^2] =4

(R+r)(R-r) = 4/Pi

Not Suff

St2
R-r = 2

Since 2 & Pi are constants, B is SUFF

So B

A slightly different way to think about it:

(1) compares area. However, area is a square function and circumference is a linear function. Therefore, depending on the numbers we select, we'll get different results.

(2) compares radius. Both radius and circumference are linear functions, so if we know the difference in radius, the difference in circumference will be constant (no matter which actual numbers we select).

(2) is suff, 1 is insuff: choose (B).

thank you - I think it's correct. (no OA)