Below is a possible solution to the Challenge 24 – Sum a Range Conditionally where Range Inputs are variables

Put following formula for the result -

=SUMPRODUCT((INDEX(INDIRECT(D1):INDIRECT(D2),,)>D3)*(INDEX(INDIRECT(D1):INDIRECT(D2),,)))

The workbook illustrating the solution can be downloaded from Solution - Challenge 24 – Sum a Range Conditionally where Range Inputs are variables