If Ms Sims can either put the books on the table in stacks of 10 or as single books.
If she decides to put them on the table in stacks of 10 (there are 2 group of 10 books and 2 single books), she can do that in the following ways:
1. group1 of 10 books, group2 of 10 books, book1, book2
2. group 2 of 10 books, group1 of 10 books, book1, book2
3. group1 of 10 books, group2 of 10 books, book2, book1
4. group 2 of 10 books, group1 of 10 books, book2, book1
which are 4 ways.
If she decides to put the books as single books there are:
n!/r!(n-r)! = 22!/1!(22-1)!=22!/21!=22*21!/21!=22 ways
So , there are 4 ways + 22 ways= 26 possible ways for Ms Sims to arrange the books on the table.
