Geometry
posted by jason .
Two points are chosen uniformly at random on the unit circle and joined to make a chord C_1. This process is repeated 3 more times to get chords C_2, C_3, C_4. The probability that no pair of chords intersect can be expressed as \frac{a}{b} where a and b are coprime positive integers. What is the value of a + b?

Please do not post Brilliant problems on this site. Thank you.