is x=0.45 a rational number
No, 45/100 is not rational because 45 cannot be evenly divided by 100.
A rational number is a number of the form a/b where a and b are both integers, so I suppose the answer is no since 0.45 is not of this form.
If however you write it in its fractional form 45/100 = 9/20, then it is.
+5265 
