Question

Joan works on commission for a furniture store. She gets a base pay of $80 a day plus 5 percent of the value of any merchandise she sells that exceeds a total of $400. Joan wrote the expression 400+0.05(t-80), where t represents her sales total in dollars, to compute the total amount of money that she will make. For sales of $475 Joan calculated that she would make $419.75.Explain Joan’s Error.