Auto fill cell range in multiple cell formulae

In a worksheet I have multiple cells using cell ranges to complete the calculations/formulae. eg "$B$40:$B$55000".

I want the numeric values of the ranges to be changeable, by not having to go and edit each of the formulae.

I was hoping to type the values into a work sheet cell e.g. type "40" and "55000" into two control cells, and reference these cells to create the range in the formula.

Then if I want a different range, I just type "50" and "50000" into the control cells.

Does anyone know how I can achieve this?