Mrs. johnson has 10 blue pens, 14 black pens, and 4 red pens in a desk drawer. if she selects two pens at random without replacing them, what is the probability that she selects a red pen and then a black pen?

There is a total of 28 pens 
probability of first getting a red pen is 4/28 or 1/7
probability of second getting black pen is 14/27 cuz one pen was already removed and not replaced so 28-1=27 
multiply 1/7 with 14/27 and you get the answer

The first one, i believe, would be correct. all the others have one thing in common, and that's that they have repeating numbers. in the second one, x and y have repeating 6's and 3's, and in the third, x and y have repeating 6's as well. in the last one, there are repeating 3's. the first one has no repeating numbers.