A box contains 8 hard-centred and 9 soft-centred chocolates. Two are selected at random. What is the probability that one is hard-centred and one is soft-centred ?
So if you pull out a soft center what is the odds? 1/17 right?
That leaves 8 hard and 8 soft, now what is you pull out a soft center? 1/16 right?
multiply them: 1/17*1/16 = 1/272