Identify the number that does not belong with the other three. explain your reasoning. negative 10 over 2, negative 13.4, square root 18, 22.7 repeating 7

The square root of 18 is the only number that is irrational.
negative 10 over 2 is -5 which can be written as -5/1  or 5/-1  (rational)
-13.4 can be written as 13.4 over 1  (rational)
22.7... can be written as fraction:  22  7/9    or 205/9 if you prefer (rational)  

Only the √18 cannot be written as a fraction since it goes on and on without repeating.  There is no number times itself that equals exactly 18.