Answer: b. 1.94
Step-by-step explanation:
For binomial distribution model , the formula to find standard deviation is given by :-
Given : The portability that the offices she visits will eventually purchase her product: p=0.25
The number of offices she visited = 20
We assume that the binomial is an appropriate model for the number of offices that make a purchase.
Then, to find the distance of the possible number of sales Tina could observe from the overall mean number of sales we find standard deviation.
Hence, the correct answer is option (b).