You wrote 0 twice so I hope this is what you mean, 0 is the answer because it cannot represent the probability of an event occurring because there is no possible number there, unlike 0.29 or 85%. Even if its a small number like 0.29 is can still represent the probability of an event occurring.
The formula for circumference is 2πr (2 times pi times the radius) 2r = d (The radius x 2 = the diameter), so the circumference also = πd (pi times the diameter)
