A circular cylindrical post with a circumference of 4 feet has a string wrapped around it, spiraling from the bottom of the post to the top of the post. The string evenly loops around the post exactly four full times, starting at the bottom edge and finishing at the top edge. The height of the post is 15 feet. What is the length, in feet, of the string?
If we could "unroll" the cylinder we would have a rectangle with a width of 4 ft and a height of 15 ft
The diagonal of this rectangle represents the length of the string and it is just the hypotenuse of a right triangle with legs of 4 and 15
Its length = sqrt (4^2 + 15^2 ) = sqrt ( 16 + 225) = sqrt (441) = 21 feet