I know your good at Maths, but sometimes you just want to double check. You can quickly check how much you will pay at the till based on the DISCOUNT off the ticket price. It is also great for when you on holiday and need to check how much something is when SALES TAX is added when you pay. The final trick is for working out the NETT amount before tax, great for claim tax back when you travel home or when submitting your expenses
If you can work it out you don't need this.