Answer:
The numbers that we have are:
26.66666..., √48, -51/2, -55.1
Now we define rational numbers as numbers that have a finite number of digits after the decimal point, or the an infinite repeating pattern of numbers after the decimal point (like the repeating 6 in the first number). These numbers can be representated as the quotient between two integer numbers.
Irrational numbers are those that have infinite digits after the decimal point, and there is no pattern.
We can see that 26.666.., -51/2 and -55.1 are rational numbers.
In the other hand, there are not two numbers that X*X = 48 (actually, if we took the fourth prime number, 7, we have 7*7 = 49)
So √48 is an irrational number, then this is the number that does not fit with the group
