3. a) You need to choose 3 questions out of a total of 10. Here the order of the words does not matter.
b) You need to pick 3 words out of the bag of 10 but here the order matters. You have 3 choices to make, so think of having three positions and determine how many possibilities there are to fill each position.
c) In part a) the order of the words does not matter but in part b) the order of the words does matter. What effect does this have on the numerical answers?