Exercise 3.9.5 from Mining of Massive Data book:

Suppose we use position information in our index, as in Section 3.9.5. Strings s and t are both chosen at random from a universal set of 100 elements. Assume J = 0.9. What is the probability that s and t will be compared if (a) s and t are both of length 9. (b) s and t are both of length 10.