There are a couple of visual/concrete models used to help student to add and subtract positive and negative numbers.
There's the thermometer...
...and the elevator...
...and the diver...
A diver rises and falls below the surface of the water. A diver can also climb out of the water on a set of stairs...
The water level is "0". So, imagine...
(-3) + (+4)
(-3) is the STARTING position of the diver. 3 steps below the water level.
+ means "and" or "then"
+ is the direction of travel. + means up
4 is the distance of travel, in this case 4 steps up
So, think of the diver starting at 3 steps below the water surface. The diver then travels up 4 steps. The diver will emerge from the water and be one step above the water surface.
(-3) + 4 = 1 (or +1)
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