There is an inverse relationship between addition and subtraction.

Example: Since 3 + 7 = 10 then the following are also true:

• 10 - 3 = 7
• 10 - 7 = 3

Similar relationships exist for subtraction.
Example: Since 10 - 3 = 7 then the following are also true:

• 3 + 7 = 10
• 7 + 3 = 10

An equation is balanced or the same on either side of the equals (=) sign. If exactly the same thing is done to both sides of the equation, it will still be balanced or equal.

In the example above we start with the equation 3 + 7 = 10:

• Subtract the same number from both sides
  3 + 7 - 3 = 10 - 3
• On the left side the 3 and -3 produce 0 which leaves
  7 = 10 - 3
• Turning the equation around to be in more normal form
  10 - 3 = 7