Question

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

Answer 1

The ancwer is 9 .nine $8 books.

Answer 2

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