Answer:
11.5 is a rational number
Step-by-step explanation:
First let's see the definition of rational and irrational.
Rational number is a number that can be written in the form of
, where q≠0.
There rational numbers have the terminating or non terminating decimals with repeating the pattern.
For example:
You can see that 3 is repeating non terminating decimals.
Irrational number is a number with non repeating decimals.
For example: 
The given number is 11.5 which is terminating decimal number.
Therefore, 11.5 is a rational number.