There was one question i got in an interview, and I couldnt answer it at all: "There are 1 million stars, and 10 planets orbiting each star. Consider that the planets do not disturb each other, and the planet systems, including the stars, dont disturb each other. Then, how many of these planets will have perfectly circular orbits?" I said that its a case of coincidence, they replied: "Scientists dont stop at coincidence, they find its probability. Please tell how we can find the answer."