Question

how do we say that there exist a rational number between two rational numbers 0.121 and 0.122?

Answer 1

Between any two rational nmbers, there are infinitely many rational numbers. For eg, bw 0.121 and 0.122 we have 0.1211 0.1212 0.12122 and so on

Answer 2

there are infinite rational number between 0.121 to 0.122
eg 0.1211,0.1212.........................................................0.122