20, without replacing the first book chosen.
25 with replacing it.
792 different groups of 5 books, in 95,040 different sequences.
30 ways.
There are only 5 places on the shelf. You have 7 books to choose from. We will ignore the order of the books on the shelf. The first place can be filled from a choice of 7 books, the next place from 6, the next place from 5, the next from 4, and the last of the 5 places from 3 books. So the number of ways of choosing the 5 is found from 7 * 6 * 5 * 4 * 3 = 2520
The answer depends on how many books on each subject there are.
5 books can be lined up on a shelf in (5 x 4 x 3 x 2 x 1) = 120 different sequences.
You can wind up with 10 different pairs of books in your hand, which you can choose from a shelf of 5 books in 20 different ways.
Choose 3 then 2 then 1; 3*2*1 = 6 ways.
792 different groups of 5 books, in 95,040 different sequences.
it depends on the shelf of course
6 ways
There are 8 ways to choose the first book There are 7 ways to choose the second book - 8 x 7 = 56 ways to select two books There are 6 ways to choose the third book - 8 x 7 x 6 = 336 way to select three books There are 5 ways to choose the fourth book - 8 x 7 x 6 x 5 = 1,680 ways to select four books.
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30 ways.
There are only 5 places on the shelf. You have 7 books to choose from. We will ignore the order of the books on the shelf. The first place can be filled from a choice of 7 books, the next place from 6, the next place from 5, the next from 4, and the last of the 5 places from 3 books. So the number of ways of choosing the 5 is found from 7 * 6 * 5 * 4 * 3 = 2520
24 ways
There are 2*5! = 240 ways.
240. 120 ways with the books stacked verticly, and 120 ways with the books stacked horizontaly, or one on top of the other.