X  is 12th from the top, Y is 17th from the bottom. Z is 20th from the top. If z is exactly between the two, then how many persons are there?

42 45 43 47

45

12 persons till X 7 persons between X and Z 1 person Z  himself 8 persons between Z and Y 17 persons Y and thereafter So, total is : 12 + 7 + 1 + 8 + 17 = 45