How many ropes did he use in a knot? You asked about the number of ropes, not the length. You can't say how many strings he used in a knot? Use as many ropes as there are ... The length of the rope is considered uncountable. Or it can be like this: How many ropes did he use in a knot? Or did he use the thread of several centenarians at a time? This should be clearer.