Let E={1,2,3,4}  and F= {1,2}. Then the number of onto functions from E to F, is _______ 

From E to F, we can define, in all $2\times 2\times 2\times 2=16$ functions (2 options for each element of D out of which 2 are into, when all the elements of E either map to 1 or to 2. Therefore, Number of onto functions = 16 - 2 = 14