Problem: in a box of 11 pens , a total of 3 are defective . if a customer buys 2 pens selected at random from the box , what is the probability that neither pen will be defective ?
Rationale: "p ( neither pen is defective ) = 8 / 11 * 7 / 10 = 28 / 55 the answer is a ."
annotated_formula: multiply(divide(subtract(11, 3), 11), divide(subtract(subtract(11, 3), const_1), subtract(11, const_1)))