Today is the only day of a sale in a clothing store. All items are reduced by 25 percent. Today a dress costs nine pound 60. How much will the dress cost tomorrow, when there is no discount?
The full price of the dress is equal to 100 percent. As the dress has been reduced by 25 percent, the sale price will be 75 percent of the full price. 100 minus 25 is equal to 75. We are told that the dress costs nine pound 60 in the sale. This means that 75 percent is equal to nine pound 60.
We need to calculate the full price of the dress, 100 percent. We can solve this problem using the method of scaling. We need to find a common factor of 75 and 100. Ideally, we find the highest common factor — in this case, that is 25 — as 25 is the highest number that divides exactly into 75 and 100.
75 percent was equal to nine pound 60. To work out 25 percent of the cost of the dress, we divide by three: 75 divided by three gives us 25. Whatever we do to one side, we have to do to the other. Therefore, we have to divide nine pound 60 by three. This is equal to three pound 20. Nine pound divided by three is three pound and 60 pence divided by three is 20 pence.
Our final step is to multiply by four. 25 percent multiplied by four is equal to 100 percent. So we need to multiply three pound 20 by four. This is equal to 12 pound 80. Three pound multiplied by four is equal to 12 pound and 20 pence multiplied by four is equal to 80 pence.
We can, therefore, say that the dress will cost 12 pound 80 tomorrow when there is no discount.