From the given diagram find the number of elements in (A${}^{{}^{\prime }}$$\cup$ B${}^{{}^{\prime }}$)

$A^{{}^{\prime }}$ will have all the elements outside the circle drawn for $A$.
So. $A^{{}^{\prime }}=$ { $2,5,7,8,9,10$ }
And $B^{{}^{\prime }}$ will have all the elements outside the oval drawn for $B$.
So. $B^{{}^{\prime }}=$ { $3,4,6,7,8,9,10$ }
Union of two sets has all the elements of both the sets.
Hence, $A^{{}^{\prime }}\cup B^{{}^{\prime }}$ { $2,3,4,5,6,7,8,9,10$ }.