Two integers m and n are chosen at random with replacement from the natural numbers 1, 2, . . . , 9. The probability that m2 − n2 is divisible by 4 is.

Such no pair are (1,3),(1,5),(1,7),(1,9),(2,4),(2,6),(2,8),(3,5),(3,7),(3,9),(4,6),(4,8)(5,7),(5,9),(6,8),(7,9). So probability is 16/36 = 4/9.Hope it clears. If u have doubts then please clearify. And if u like my answer then please approve answer