Final answer:
The question lacks the necessary details about Plan A's billing structure, making it impossible to determine the number of texts corresponding to a monthly bill of $22.50.
Step-by-step explanation:
The question does not provide enough information to determine how many texts a customer on Plan A sent to receive a bill of $22.50. To answer how many texts she sent, we would need more details about the pricing structure of Plan A—specifically, the cost per text or any included amount of texts in the base price before additional charges apply.
Regarding the other parts of the information provided, they refer to different contexts such as average texts sent per day, probabilities related to sending texts, and sample sizes for statistical confidence. These pieces of information are unrelated to determining the number of texts corresponding to the monthly bill of the customer on Plan A without additional details on the plan's billing structure.