A fireman stood on the middle rung of a ladder pouring water on a burning building. As the smoke cleared, he stepped up three rungs. But a sudden flare-up forced him to go down five rungs. He later climbed seven rungs and worked until the fire was out. At that point, he climbed the last six rungs and entered the building. How many rungs were on the ladder?
Draw a good picture of a ladder with many rungs, and follow the action in reverse.
There must have been 23 rungs total (he started on the 12th).