We choose a positive divisor of 20^20 at random (with all divisors equally likely to be chosen). What is the probability that we chose a multiple of 10^10?
20^20 has 861 divisors. 10^10 has 341 divisors. Only 20 multiples of 10^10 are divisors of 20^20 and they are all powers of 2. From 2^1 x 10^10 to 2^20 x 10^10
