20.A firefighter spraying water on a fire stood on the middle of a ladder. The smoke lessened, so she moved up 3 rungs . It got too htot, so she backed sown 5 rungs. later, she went up 7 rungs and stayed until the fire was out. then, she climbed the remaiming 4 rungs and went into the building . How amny rungs does the ladder have/
from the middle to the top:
+3-5+7+4
double that
To find out the number of rungs on the ladder, let's break down the firefighter's movements step by step:
1. Start: The firefighter is standing on the middle of the ladder. We don't know the total number of rungs yet.
2. First movement: The firefighter moves up 3 rungs from the middle position, so she is now 3 rungs from the top.
3. Second movement: The firefighter moves down 5 rungs, so she is now 2 rungs from the bottom (5 rungs down from the middle position).
4. Third movement: The firefighter moves up 7 rungs, so she is now 5 rungs from the top (2 rungs up from the previous position).
5. Final movement: The firefighter climbs the remaining 4 rungs to reach the top.
Based on these movements, we can conclude that the firefighter moved from 3 rungs from the top to reach 5 rungs from the top, which means there are a total of 8 rungs on the ladder.
Therefore, the ladder has 8 rungs.