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.

48:7 25:8 15:4 8:3

25:8

The logic followed here is : IInd number2 - 1 =  Ist number 48:7 → 72 - 1 = 48 25:8 → 82 - 1 = 63 (odd) 15:4 → 42 - 1 = 15 8:3 → 32 - 1 = 8