One asks me to offer a simplified probability calculation technique to this question:

Activity 1 has an optimistic estimate of 7 days, a most likely estimate of 16 days and a pessimistic estimate of 25 days. What is the approximate calculated probability that the activity will be finished in 10 to 22 days?

 A. 95.4%
 B. 50.0%
 C. 99.7%
 D. 68.3%