The laundry detergent that I normally buy costs £6.40 for a 2-litre bottle and always lasts for 32 washes. Last month I decided to try a new brand that is £1.40 more expensive and contains 2.5 litres. However, because of the amount that I have had to use to get my clothes properly clean, it has run out after only 25 washes. Based upon my experience, by how many pence per wash is my normal detergent better value than the new brand?