Shampoo is sold in two sizes. 1) 500 ml for £1.98 2) 3 litres for £12.80 (now 15% off). Which is better value for money?

Firstly we need to work out the new price of the 3 litres of shampoo after 15% has been taken off.  Let's use the three step method for percentages. 100% is £12.80 £12.80/ 100= £0.128     1% is £0.128 £0.128 x 85= £10.88     85% is £10.88 Then we need to compare the price of the two bottles per 500ml.  £10.88 / 6 = £1.81 compared to £1.98 Therefore we can see that the 3 litre bottle is better value for money.