Whether it's temperature, altitude, or bank balances, this is an essential concept for expressing 'in which direction and how far from the reference point (0)'.
Think of the sea level as 0. Anything above the sea (like a flying bird) is positive (+), and anything below the water (like a swimming fish) is negative (-). Addition (+) means moving UP, and subtraction (-) means moving DOWN.
Many people get confused about why 'subtracting a negative number' is the same as addition. Subtraction means 'turn around', and negative means 'move backward'. So, 'turning around and moving backward' results in moving forward (addition).
Formula
Let's check your understanding!
Historically, negative numbers only became commonly used in mathematics relatively recently (around the 17th century). Before that, it was believed that 'numbers smaller than 0 do not exist', and they were only treated as special symbols for recording debt.