they did count in tens, as most civilizations did, though not exactly in "decimal". so 2345 would be either written out as MMCCCXXXXIIIII (but replace the letters with hieroglyphs), or sometimes spelled out phonetically. they had words for twenty, thirty and so on.

so obviously they can factor numbers and they know eighteen is 2*9 and twenty is 2*10 and that they can simplify when dividing 18 by 20, it's just that they don't consider 9/10 a finished result.