# math

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kyle had 36 books in hislocker. some were library books, some were textbooks, and the rest were telophone books. the number of library books and textbooks combined equal twice the number of textbooks. the number of textbooks and telephone books combined equals three times the number of library books. how many of each type of book were in kyle's locker??

• math -

Do it this way

a=library books
b=textbooks
c=telephone books

You know a + b + c = 36
You know that a + b = 2b (library books plus textbooks equals twice number of textbooks)
You know that b + c = 3a (textbooks plus telephone books equals three times number of library books)

Take equation #2 a+b=2b
Subtract b from each side
a=b The number of library books equals the number of textbooks

Take equation #3 b+c=3a Substitute a for b since you know now from equation #2 that a=b Now you have a+c=3a
Subtract a from each side c=2a

Now, go to equation #1 a+b+c=36

You know a=b
You know c=2a
substitute
a + a + 2a = 36

Combine like terms and divide
4a = 36 a= 9

Again, you know a = b and c= 2a therefore a=9, b=9, c=18
9 library books
9 text books
18 telephone books