• Printer Friendly Version

Subject

Math, Science & Technology

Description

There is an inverse relationship between the operations of addition and subtraction.
If you take the math fact, 5 + 6 = 11, then the following mathematical statements are true:

• 11 - 5 = 6
• 11 - 6 = 5

A similar relationship exists for a subtraction math fact. If you have the math fact, 10 - 6 = 4, then the following mathematical statements are true:

• 4 + 6 = 10
• 6 + 4 = 10

This relationship is true because we are dealing with equations. 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 4 + 6 = 10.

• Subtract the same number from both sides 4 + 6 - 4 = 10 - 4.
• On the left side the 4 and -4 produce 0 which leaves 6 = 10 - 4.
• Turning the equation around to be in more normal form 10 - 6 = 4.

Related Academic Standards

New York State

NY-2.OA.2a Fluently add and subtract within 20 using mental strategies. Strategies could include:

• counting on;
• making ten;
• decomposing a number leading to a ten;
• using the relationship between addition and subtraction; and
• creating equivalent but easier or known sums.

NY-2.OA.2b Know from memory all sums within 20 of two one-digit numbers.

NY-2.NBT.5 Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.

NY-2.NBT.7a Add and subtract within 1000, using

• concrete models or drawings, and
• strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.

Relate the strategy to a written representation.

NY-2.NBT.7b Understand that in adding or subtracting up to three-digit numbers, one adds or subtracts hundreds and hundreds, tens and tens, ones and ones, and sometimes it is necessary to compose or decompose tens or hundreds.

View All