If the number 3 were added to the set 2 3 3 3 4 5 5 which central tendency would change

The centers tendency would decrease as 3 is
For one, a prime
And two, on the lower end of the central reoccurrence

Prior to adding 3, let's find the mean and the median:

Mean = X̅ = (2+3+3+3+4+5+5)/7 = 25/7 = 3.571
Median = 3

After adding a 3, the New Mean becomes X̅₁ =    (2+3+3+3+3+4+5+5)=7/2 =3.5
And the Median is again 3
So the Mean X̅ slightly changed