All three facts are dead simple on their own. The trap is that the diagrams look similar, so it's easy to grab the wrong rule on autopilot. The fix is to read the picture before you reach for a number.
Trap One — 180 When It Should Be 360 (or the Reverse)
The giveaway is whether the angles sit on a straight edge or fill the whole turn. If you can see a flat line running straight through the point, the angles on one side of it add to 180°. If the angles fan out and there's no straight line splitting them — they go right around — it's 360°. Ask yourself: "is there a straight line here, or a full circle?"
Trap Two — Subtracting When Angles Are Equal
This one stings. When two straight lines cross to make an X and x is the angle directly opposite a known one, the answer is just equal — if the known angle is 70°, then x is 70°. The trap is doing 180 − 70 = 110 out of habit. That 110° is real, but it's the neighbour angle, not the opposite one. Opposite = equal. Next-door = adds to 180.
Trap Three — Adjacent vs Opposite
In any X-cross there are four angles. Adjacent angles (the two side by side) sit on a straight line, so they add to 180°. Vertically opposite angles (the two facing each other) are equal. Same diagram, two different relationships — so before you write anything, decide which pair you're actually looking at.