Question:

Can you please explain me how the answer is 99.73%

An activity has an optimistic estimate of ten days, pessimistic estimate of sixteen days,
and most likely estimate of thirteen days. Assuming a normal distribution,
what is the probability that the task will be completed within 10 to 16 days?

99.99 %
99.73 %
95.46 %
68.26%

Ans : 99.73%