What is the answer to 13 in precise detail?

Well, I don't know.  Let's see . . . . .

First draw: One 'M' available out of 11 letters.   Probability of picking it = 1/11.
2nd draw:  Four 'I's available out of 10 letters.  Probability of picking one = 4/10.
3rd draw:  Four 'S's available out of 9 letters.   Probability of picking one = 4/9.
4th draw:  Three 'S's available out of 8 letters. Probability of picking one = 3/8.
5th draw:  Three 'I's available out of 7 letters.  Probability of picking one = 3/7.
6th draw:  Two 'S's available out of 6 letters.   Probability of picking one = 2/6.
7th draw:  One 'S' available out of 5 letters.     Probability of picking it = 1/5.
8th draw:  Two 'I's available out of 4 letters.     Probability of picking it = 2/4.
9th draw:  Two 'P's available out of 3 letters.   Probability of picking one = 2/3.
10th draw: One 'P' available out of 2 letters.   Probability of picking it = 1/2.
11th draw: One letter left.  It is an 'I'.  Probability of picking it = 1 .

Probability of all of those draws in order =

    (1/11) x (4/10) x (4/9) x (3/8) x (3/7) x (2/6) x (1/5) x (2/4) x (2/3) x (1/2) x (1) =

           1,152 / 39,916,800 =

                 1 / 34,650 =

                                     0.00002886 =

                                     0.002886 percent (rounded)

Not a good bet.  (But better than the lottery.)

The slope of the function is 0.5.