The 2nd competitor ate twice the amount of the 1st competitor's 12 hot dogs So he ate 2*12 = <<2*12=24>>24 hot dogs
The 3rd competitor ate 25% less than the 2nd's 24 hot dogs, which is 24/4 = 6 hot dogs
If the 2nd competitor ate 24 hot dogs, and the 3rd ate 25% less than that, then the 3rd competitor ate 24 - 6 = <<24-6=18>>18 hot dogs
#### 18