I'm assuming you were given these four values
50.1, -50/2, -50.1, sqrt(50)
where 'sqrt' stands for 'square root', and the slash symbol means divide or fraction.
If my assumption is correct, then the term that does not belong is sqrt(50). This is because the other values are all rational. We can express them as a fraction of two whole numbers
- 50.1 = 501/10
- -50/2 is already a fraction, no need to do any work for this one
- -50.1 = -501/10
But we can't do the same with sqrt(50). It is irrational. Note how 50 is not a perfect square. Your calculator will show that sqrt(50) = 7.07106781186548 and that decimal sequence goes on forever without any pattern. If you were given sqrt(49), then it would work because sqrt(49) = 7 = 7/1.