This brain teaser shows four boxes with letters A, C, G, and one missing letter.
At first, it looks like a simple alphabet sequence, so many guess B. But the trick is to use letter positions:
A = 1
C = 3
G = 7
Now look at the pattern:
1 → 3 (+2)
3 → 7 (+4)
The pattern doubles each time, so the next step is +8:
7 + 8 = 15
The 15th letter is O.
So the missing letter is O, following the pattern of doubling differences: +2, +4, +8.