I have a problem that I hope someone can help me with.

I have a map with a standard numerical x,y co-ordinate system. Within the map I have regions that are all the same size e.g. co-ordinates 0,0 to 19,19 are Region A; 20,20 to 39,39 are Region B going up to 99,99 in Region E then continuing in the next 'row' of regions such that co-ordinates 0,20 are in Region F; 24,49 are in Region L etc.

I want excel to return the region when a set of co-ordinates are entered. Now for a small map with only a few regions I can use the IF and AND/OR functions.

However my map is now 500 x 500 squares and the regions are 50 x 50 squares (i.e. 100 regions going from Region 1 to 100 in a 10 x 10 array). I can't figure out if there is a relatively simple formula to achieve this.

Any suggestions?