A fireman is on the middle step of a ladder. (There are the same number of steps above him as below him.) If he goes down 4 steps, then up 7 steps, and then down 13 steps, he will be on the first step above the ground. How many steps does the ladder have?
10 is the direct middle if you go down 4 that is 6, if you go back up 7 you get 13 and if you go back down 13 and you are on the first step 13-13 is 0, so the ladder has 20 steps.
