in a box of 11 pencils , a total of 2 are defective . if a customer buys 3 pencils selected at random from the box , what is the probability that neither pencils will be defective ?
"first , there are 9 c 3 ways you can select 3 good pencils from 4 good ones . second , there are 11 c 3 ways you select 3 pencils from 6 ones in the box . then , the probability that neither pen will be defective is : 9 c 3 / 11 c 3 = 84 / 165 = 28 / 55 answer is b"
divide(divide(factorial(subtract(11, 2)), multiply(factorial(subtract(subtract(11, 2), 3)), factorial(3))), divide(factorial(11), multiply(factorial(subtract(11, 3)), factorial(3))))