Transcript

NARRATOR:

In some situations, you may be given the total after the discount or VAT has been applied and asked to find the original amount. For example, suppose an online shop charges an extra 5% of the cost of purchases for postage and packing. You have a gift voucher for 30 pounds. What is the maximum you can spend at the shop so that the total, including the postage, is less than 30 pounds? The cost of your purchases is 100%, as it is the whole value being dealt with. And the postage is an additional 5%. Therefore, 105% is equal to 30 pounds. We know the most you can spend is 30 pounds. So that would mean the 105% is equal to the 30 pounds.

Let's start by working out what 1% would be. Since 105% is 30 pounds, 1% is 30 pounds divided by 105. That's about equal to 0.2857 pounds to 4 decimal places. We now want to know what amount in money 100% corresponds to because that will tell us what we can buy.

Since 1% is 0.2857 pounds, 100% is 0.2857 pounds times by 100. That's equal to 28.57 pounds. The maximum amount that can be spent then is, 28.57 pounds.