Explain how to resolve this problem. there are 13 books. some books cost $9 each and the rest cost $8 each. A total of $108 spent for all 13 books. how many $8 books were on the table.

the answer is actually 9. nine $8 books totals $72 and four $9 books total $36. $72+$36=$108. and 9+4=13 books

X=one type that cost 9

y=one type that cost 8

total books=type1+type2

total books=13

x+y=13

the total cost=cost of each added together

cost of each=number of books times cost per book

total cost=108

9x+8y=108

we have

x+y=13

9x+8y=108

solve for x and y

multiply first equation by - 8 and add to first equation

-8x-8y=-104

9x+8y=108 +

x+0y=4

x=4

subsitute

x+y=13

4+y=13

minus 4

y=9

4 of the $9

9 of the $8

thats how to solve

The ancwer is 9. nine $8 books.