Sofia will attend either 1 or 2 sessions on her last day.
On any other day, she will attend exactly 2 sessions.
Question: At the end of the third day of attending training sessions, how many sessions will Sofia has left?

Statement 1 The sequence of training sessions Sofa will attend will last 6 days.
For the first 5 days, she would have covered 2 sessions per day * 5 days = 10 sessions
If she attends 1 session on the last day (6th day), then;
total training session = 10+2 = 12 sessions.
Session covered at the end of the third day = 2 sessions per day * 3 days = 6 sessions

Since we do not know the exact total session, we cannot find the sessions left for Sofia to attend. Hence, statement 1 is NOT SUFFICIENT.

Statement 2 There are a total of 11 training sessions in the sequence of the training session Sofia will attend.
Since training session per day = 2 (except for last day)
Total days for training = 11/2 = 5 remainder 1.
Sofia will spend 5 days attending 10 training sessions.
Given that she can either attend 1 or 2 training sessions on the last day, her last day will be the 6th day and she will attend just one training session to make a total of 11 training sessions.
At the end of the third day, she would have attended a sequence of 6 training sessions.

Total session left = total training session - training session for 3 days
= 11 - 6 = 5 training sessions left
So, statement 2 alone is SUFFICIENT.

The answer is, therefore, option B.