Answer :
25% off means the new price of the item is 75% of the originl price ( 100% - 25% = 75%)
Multiply the original price by 75%:
20 x 0.75 = 15
The sale price is £15
25% off means the new price of the item is 75% of the originl price ( 100% - 25% = 75%)
Multiply the original price by 75%:
20 x 0.75 = 15
The sale price is £15