There has been a house on fire. The fireman is now standing in the middle rung of the ladder and trying to extinguish the fire. He climbs 6 rungs more but the heat and deadly flames make him climb down 10 rungs. When the fire is settling gradually, he climbs 18 rungs and reaches the top of the ladder for better access to the house.

Calculate the number of rungs in the ladder ?

29 rungs

Suppose he is standing on m at first which is the middle rung.

He climbs 6 rungs which makes his position to be m+6.

He climbs down ten rungs which makes his position to be (m+6-10) = m-4

He climbs 18 rungs to reach the top t which makes his position (m-4+18) = m+14

Now, m+14 = t

Which means there are 14 rungs above the middle rung and 14 rungs below the middle rung. Counting the middle rung as well, it makes a total of 29 rungs.