Usually, no sign before the bracket means juxtaposition. Scientific calculators do account for it, while regular ones may not.

So 2(1+2) is really (2+4)

Compare 2/2x and 2/2×X where x is (1+2)

The first is 2/(2+4)=1/3, the second is (2/2)×(1+2)=3

Also, there’s no real rule about solving left to right due to associative and commutative properties: 1×2×3 = 1×(2×3) = (1×2)×3 = 3×1×2 = 2×1×3 = 6