A survey of households in a major city found that:

- 96% had colour televisions

- 65% had computers

- 51% has dishwashers

- 63% had colour televisions and computers

- 49% had colour televisions and dishwashers

- 31% had computers and dishwashers

- 30% had all three

a.) List the categories of households not included in these survey results.

b.) Use a Venn diagram to find the proportion of households in each of these categories.