Harry and Tom each had a set of 21 snooker balls, 15 red and 6 coloured. Each of them had a bag into which he put one or more of the red balls, and three or more of the coloured balls from his set. Though Tom put more balls in his bag than Harry put in his bag, each of them calculated that if he picked three random balls out of his bag simultaneously there was a 1 in X chance that all three would be coloured. X represents the same number for each of them. What is the value of X ?