The second number in the given number-pairs is obtained by performing certain mathematical operation(s) on the first number. The same operation(s) are followed in all the number-pairs EXCEPT one. Find that odd number-pair.
Answer & explanation
Correct answer: option 1
The logic;
1) 1 : 2;
If we add 1 to 1 we get 2
2) 3 : 5;
If we add 3 to 3 we get 6 not 5
3) 7 : 25;
If we add 7 to 7 we get 14 not 25
4) 5 : 13;
If we add 5 to 5 we get 10 not 13
Thus, 1 : 2 is correct.