The minimum number of persons in the queue.  What’s given in the problem  There are (5) persons between A and B. There are (8) persons between B and C. There are (3) persons ahead of C. There are (21) persons behind A.  Helpful information  To minimize the number of people, B should be between A and C.  How to solve  Calculate the minimum number of persons in the queue by considering the overlapping arrangement.Step 1 . Determine the relative positions of A, B, and C for the minimum number of persons For the minimum number of persons, B must be between A and C. The order is C, B, A. Step 2 . Calculate the number of persons between C and A Persons between C and A = Persons between C and B + Persons between B and A + 2(for B and C) Persons between C and A = (8+5+2=15)
Step 3 . Calculate the total number of persons in the queue Total persons = Persons ahead of C + Persons between C and A + Persons behind A + 1 (for A) Total persons =(3+15+21+1=40)
Solution 
The minimum number of persons in the queue is (28).