Answer:
C:300
Explanation:
We are given that each participants in a certain study was assigned a sequence of 3 different letters from the set {A,B,C,D,E,F,G,H}
Number of letters =n=8
We are given that number of possible sequence were not assigned =36
We are given that no sequence was assigned to more than one participant.
We have to find that number of participants in the study
Permutation formula :

We have r=3
Using the permutation formula
The number of sequence were assigned =

The number of sequence were assigned =

The number of sequence were assigned =336
But we are given that 36 of possible sequence were not assigned
Therefore, required number of sequence were assigned=336-36=300
Number of sequence assigned=Number of participants
Therefore, number of participants in the study=300
Answer:C:300