Ivan has six ropes. Each strip is 25 cm long. He tied these knots together to form a new rope 90 cm long. Each knot on the new rope uses the same length as the original rope. What is the length of the original rope he uses for each knot? The answer is to use 2 cm, which is equivalent to six ropes connected end to end to form a long rope.

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.