book Maths Puzzle Numerical Ability

x^-1+y^-1?x^-1y Can you help me simplify?

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MUST SOLVE USING PERMUTATIONS</b>

On a bookshelf there are 9 books. In how many ways can you select 4 books to read in order?

I would greatly appreciate your assistance with this problem. I think I have the answer---But not the formula. I've worked on this for days, HELP PLEASE!!!!!!!!!
Alex has four bags weighing 1,2,3 and 4 pounds. To arrange them, he will pic