Problem: bag contains 7 green and 8 white balls . if two balls are drawn simultaneously , the probability that both are of the same colour is - .
Rationale: explanation : drawing two balls of same color from seven green balls can be done in â  · c â ‚ ‚ ways . similarly from eight white balls two can be drawn in â  ¸ c â ‚ ‚ ways . p = â  · c â ‚ ‚ / â ¹ â  µ c â ‚ ‚ + â  ¸ c â ‚ ‚ / â ¹ â  µ c â ‚ ‚ = 7 / 15 a
annotated_formula: divide(add(divide(factorial(7), multiply(factorial(subtract(7, const_2)), factorial(const_2))), divide(factorial(8), multiply(factorial(subtract(8, const_2)), factorial(const_2)))), divide(factorial(add(7, 8)), multiply(factorial(subtract(add(7, 8), const_2)), factorial(const_2))))