Since you are arranging, not just selecting, the correct answer is not 7C4 but 7P4 = 7!/3! = 840.(ex) A student has 7 different textbooks. How many different ways of selecting and arranging 4 books on a shelf are there?
I do seven choose four to get 7C4 = 35. But, the answer key says 210.
How do you get the answer? Thanks a lot.