There are
17
books on a shelf.
8
of these books are new.
(a) what is the ratio of all books to used books?
(b) what is the ratio of new books to used books?

17 books in total, and 8 new. To find the number of used books, we subtract 8 from 17.

17-8= 9 used books

Now we have 8 new books and 9 used books.

All books: 17
Used books: 9
New books: 8

(a) all books: used books
     17: 9

(b) new books: used books
     8: 9

Okay so for every triangle has three angles that always add up to 180 degrees. and to tell the difference between whether they are secure, right or obtuse is that acute: has one angle that is less than 90 degrees. right triangle means there is at least one angle that is exactly 90 degrees. and an obtuse angle has an angle that is bigger than 180 degrees. i’ll do #13 as an example: 13. 40 and 50 so if every triangle has 180 degrees 40+50= 90 degrees then180-90= 90 degrees so the third angle is 90 degrees and because this triangle has a 90 degree angle it means it is a right triangle