Answer
19 rungs
Work Step by Step
The firefighter started on the middle rung. (I drew this problem out just labeled it “middle” to start).
He climbed up 4 rungs. I labeled the rung above the middle as “1” and went up from there to “4”. We know there is a middle rung plus 4 rungs above it.
He then went down 6 rungs. (The first 4 he went down took him back to middle), then the next two (so that he went down 6 rungs) put him 2 below the middle.
He then climbed up 7 rungs and stayed until the fire was out. The first 2 rungs took him to the middle rung. Then to finish going up the 7 rungs, he ended up 5 rungs above the middle one.
Last, he climbed up 4 more rungs and entered the building. He was already 5 above the middle, so going up four more rungs put him 9 above the middle.
There were 9 rungs above the middle rung and 9 rungs below the middle rung. And, we must also count the middle rung. 9 plus 9 plus 1 is 19.
