Three of the following four number triads are alike in a certain way and thus form a group. Which is the number triad that does not belong to that group? (NOTE: Operations should be performed on the whole numbers, without breaking down the numbers into its constituent digits. E.g. 13 – Operations on 13 such as adding/subtracting/multiplying etc. to 13 can be performed. Breaking down 13 into 1 and 3 and then performing mathematical operations on 1 and 3 is not allowed.)

Correct option is A

Logic = First + 15 = Second
Second - 6 = Third
Let’s apply this logic to each triad:
Triad A: 31 - 46 - 41
31 + 15 = 46 
46 - 6 = 40 not 41
So, Triad A follows the pattern.
Triad B: 29 - 44 - 38
29 + 15 = 44 
44 - 6 = 38 
So, Triad B follows the pattern.
Triad C: 24 - 39 - 33
24 + 15 = 39 
39 - 6 = 33 
So, Triad C follows the pattern.
Triad D: 17 - 32 - 26
17 + 15 = 32 
32 - 6 = 26 
So, Triad D follows the pattern as well.

Option B, C and D follows the logic properly except option a.

hence option a is odd one out.