Question

How many ways can 3 books be placed on a shelf if chosen from a selection of 7 different books?

Answer 1

so at first, you have 7 choices since none of them have been chosen
when you pick the second book, you now have 6 choices
when you pick the third book, you now have 5 choices

so the answer is 7 times 6 times 5 choices=210 choices