What Digit Is At ? in This Series 57431 12265 665? 12

Answer: 7

Explanation:

Sum of numbers in
10,000’s place = 5 + 1 = 6
1,000’s place   = 7 + 2 + 6 = 15 = 1 + 5 = 6
100’s place      = 4 + 2 + 6 = 12 = 1 + 2 = 3
10’s place        = 3 + 6 + 5 + 1 = 15 = 1 + 5 = 6
1’s place          = 1 + 5 + ? + 2

By symmetry (6 6 3 6 ?) of the numbers, sum in 1’s place must be 6.

Only if ? is 7, sum would add up to 6.