In a best buy question, you are not looking for the lowest total price. You are looking for the option that gives the lowest cost for the same amount of product.

A useful method is:

1. Read the price and amount for each option.
2. Adjust any offers so you know the total cost and total amount.
3. Choose a fair unit to compare, such as per item, per kg, per 100 g, or per 100 ml.
4. Convert to pence if that makes the arithmetic easier.
5. Calculate the unit price for each option.
6. Compare the unit prices.
7. Pick the option with the smaller unit price.