What type of number cannot be found on a number line?

Question

What type of number cannot be found on a number line?

Answer 1

infinity is the only think I can come up with

Answer 2

imaginary numbers

Answer 3

Imaginary numbers (unless your number line is the set of imaginary numbers).

Answer 4

imaginary

Answer 5

All real numbers occupy a specific point on a number line.  However if the number is irrational, it would be physically impossible to pinpoint its exact location since irrational numbers have non-repeating, non-terminating decimal representations.  For example, you could never locate the exact location of pi.  Any finite representation of pi (3.1415926 for example) is less than the actual value of that number.  But pi does live somewhere between 3.14 and 3.15 on the number line.  

Imaginary numbers (those of the form a + bi, where b is not equal to 0) do not occupy a position on a number line.  Rather, they inhabit the complex plane (two-dimensional).

Finally, infinity is not a number.  Therefore, it cannot be part of this discussion.