Adding and Subtracting Decimals
When you add and subtract decimals:
1. Make sure you align the decimal points.
2. Then add or subtract as usual
3. The decimal point will appear directly below its place in the problem.
When you subtract a decimal from a whole number:
1. Place a decimal point after the whole number
2. Align the decimal points
3. Annex (insert) as many zeroes to the right as needed to have the same number of decimal
places
Properties of Addition
Identity Property of Addition- the sum of zero and a number is that number
Ex. 5.6 + 0 = 5.6
Ex. x + 0 = x
Commutative Property of Addition- Changing the order of the addends does not change the sum
Ex. 3.1 + 4.2 = 4.2 + 3.1
Ex. a + b = b + a
Associative Property of Addition- changing the grouping of the addends does not change the sum
Ex. (2 + 3) + 4 = 2 + (3 + 4)
Ex. (a + b) + c = a + (b + c)