CFA Level I Mock Exam Afternoon Q17 and Q20 numbers, between, solution, following, position

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Q17 (A) Use of abbreviations
Why is this choice wrong? I think it's OK to use CFA for Charted Financial Analyst.

Q20 solution is (B)

The 10 numbers are:
-11, -5, 8, 9, 18, 20, 20, 21, 25, 35
Shouldn't we use the following to calculate the position of an observation in a given percentile:

(1+N)*(percentile) = (1+10)*80% = 8.8
so the number is somewhere between the 8th and 9th number which is
21 + 0.8*(25-21) = 21 + 3.2 = 24.5
that is (C)

Can someone please help me with these two problems?