We can insert infinite rational numbers between any given rational numbers .it is called density property
16 rational numbers between 2.1 and 2.2 = 2.11 , 2.115 , 2.12 ,2.125 , 2.13 , 2.135 , 2.14 , 2.145 , 2.15 , 2.155 , 2.16 , 2.165 , 2.17 ,2.175 , 2.18 , 2.185