Let R be a relation from A = {1, 2, 3, 4} to B= {1, 3, 5} such that R = {(a, b) : a < b, where a$$\in$$A and b$$\in$$B}. What is RoR^$$-$$1 equal to?

What is the number of natural numbers less than or equal to 1000 which are neither divisible by 10 nor 15 nor 25?

Suppose, there is a relation * between the positive numbers x and y given by x * y if and only if x $$\le$$ y². Then, which one of the following is correct?

Let R be a relation on the set N of natural numbers defined by 'nRm $$\Leftrightarrow$$ n is a factor of m'. Then, which one of the following is correct?