Number analogy section deals with two types of questions:
I. Choosing a similarly related pair as the given number pair on the basis of the relation between the numbers in each pair.
II. Choosing a number similar to a group of numbers on the basis of certain common properties that they possess.
8 : 81 : : 64 : ?
The relationship is x^ : (x + 1)(^+1).
Now, 64 = 43
So, required number \ (4 + 1)(3+1) = 53 = 625.