Over the course of a year Mr and Mrs Jones and their two sons spend an average of £120 a week at the local supermarket. 70% of this spending is the weekly family food bill, 20% goes on household goods and the final 10% on store cupboard ingredients. When their daughter returns from her gap year to live at home the weekly food bill increases by 20% and their spending on household goods goes up 5%, whilst they continue to spend the same on store cupboard ingredients.