lets say kevin bought a book for 40% of his money. Kevin has X dollars how do you write this as a math thing.
.40x
If Kevin had X amount of money, then:
40% of X or 40%X, Kevin would have spent on his book. So, the equation would look like this this:
X - 40%X=$ amount of money remaining in his pocket.
X - 40/100X=$
X - .40X=$ money left.