Answer: 51.54 ft
Step-by-step explanation:
The ladder should be 1 feet away from the wall by each 4-feet that the wall rises, so if we have a 50 ft wall, the distance between the bottom of the ladder and the wall must be:
50ft/4 = 12.5ft.
Now we know the cathetus of our ladder, 12.5ft and 50ft, let's find the hypotenuse, that is:
H = √(12.5^2 + 50^2) = 51.54 feet.
Which is also the lenght of our ladder, so the shortest ladder to climb safely a 50 ft wall is 51.54 ft long.