Answer: The required probability that Maria will wear blue dress at her party is 16.67%.
Step-by-step explanation: Given that Maria has three red dresses, two white dresses and one blue dress.
We are to find the probability that Maria will wear a blue dress at her party.
Let S denotes the sample space of selecting a dress from the collection of Maria and A be the event that Maria wear blue dress at her party.
Then, we have

Therefore, the probability of event A is given by

Thus, the required probability that Maria will wear blue dress at her party is 16.67%.