To get the answer we have to find 55% of 9. First step is rewrite 55% as 0.55 Second and the last step is to multiply 0.55 times 9 0.55*9=4.95~=5 -its the answer
Firstly, you should find 10% of 9, which is 0.9
You've then got to multiply this by 5.5, as you've got 55 books.
0.9x5.5= 4.95
Therefore, as you cannot have .95 of a books, this has to be rounded to 5.
Therefore, the library has 5 books out on the topic.
Hope this helps :)