Is 21.192 a rational or irrational

Rational number is something that does not have a decimal number going to infinity or something that can be written as a fraction

21.192 can be written as 21 192/1000 so yes its rational

i.e. √2 goes on forever and cannot be written as a fraction. so no it is not rational. it is irrational just like π.

Hope this helps :P