29.99 * .20= 5.998
29.99- 5.998 = she payed 23.99
25* .10= 2.50
25-2.50= he payed 22.50
therefore he got the better deal
the "verticle" line test is used to determine if a graph represents a function.
this is due because functions have to contain one output and not multiple, and this can be tested with the vertical line test. hope this !