1. A particular type of chocolate bar comes in a packet of 10. Each individual chocolate bar inside the packet has a coloured wrapper. The colour of the wrapper for each chocolate bar is assigned at random.

The mean number of chocolate bars with a purple wrapper in a pack of 9 bars is 4.

Vivienne suggests that the number of chocolate bars with purple wrappers in a pack of 9 chocolate bars can be modelled by a binomial distribution.

Consider the conditions required for a binomial distribution and explain why Vivienne's suggestion is appropriate.