Find the missing number?

Solution (By Examveda Team)

Working from left to right, numbers represent the reverse alphabetical values of the vowels in the alphabet. I.e There are 5 Vowels A, E, I, O, U.

A = 1 = Reverse alphabetical number = 26.
E = 5 = 22
I = 9 = 18
O = 15 = 12
So,

U = 21 =6.
Missing Number = 6.