Problem: an urn contains 6 red , 5 blue and 2 green marbles . if 2 marbles are picked at random , what is the probability that both are red ?
Rationale: option ( b ) is correct p ( both are red ) , 6 c 2 / 13 c 2 = 5 / 26 answer b
annotated_formula: divide(divide(multiply(6, 5), const_2), divide(multiply(add(add(6, 5), 2), subtract(add(add(6, 5), 2), const_1)), const_2))