Set up an equation when x is the cost of a book. If we know that 45 + 5 = 50:
45x = 50(x - .1)
Now, multiply across the parentheses:
45x = 50x - 5 (Now, combine terms over the equal sign)
-50x -50x
-5x = -5 (Now, divide off the -5 from both sides)
/-5 /-5
x = 1
This means that the current cost of a book is $1. This works out if you test it.
Hope this helps!
~ArchimedesEleven
