world problem to find sales tax

Question

the amount of tax T paid on a product is directly proportional to its purchase price P. In Indiana the sales tax on a sony reader that sells for $260 is $17.50. What is the sales tax on an e-book that sells for $21? round to the nearest cent

Answer 1

Set it up as two fractions equal to each other.  260/17.50 = 21/x.  Then you cross-multiply.  260x = 17.5 * 21.   260x = 367.5.  Divide both sides by 260.  x = 1.41.  $1.41 is your tax.