The second number in the given number-pairs is obtained by performing certain mathematical operation(s) on the first number. The same operation(s) is/are followed in all the number-pairs, except one. Find that odd number-pair.

9 : 100

The logic followed here Is :

(Ist number  - 1)² = second number

12 : 121 =  12 - 1 = (11)² = 121

6 : 25 =  6 - 1 = (5)² = 25

9 : 100 =  9 - 1 = (8)² = 64 ≠ 100

8 : 49 =  8 - 1 = (7)² = 49