How can I identify witch of those numbers don’t belong with the other there 50.1 -50 over two -50.1 square root of 50?

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

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.

if you are saying purchasing 3 social media ads and one newspaper ad counts as one purchase then there are:

6 purchases

if you are asking how many of each then:

18 social media ads

6 newspaper ads