Math 6 A (Periods 1 & 2)

Adding & Subtracting Decimals 3-6

Rules

1) Write the given numbers one above the other with the decimal points in line

I call that “Stack’ Em”

2) Add any zeros to get the same number of decimal places and then add or subtract ( +/-) as if the numbers were whole numbers.

We put the added zeros in colored pencil to distinguish them!

3) Place the decimal point in the number for the sum or difference in position directly under the decimal points in the given numbers.

add 6.47 + 3.40.8 + 73.523

Stack them   Lining up the decimals

420.793

Subtract 13.94 – 7.693

Again, stack and align the decimal points

6.247

Chelsea (Lindsey) had $ 317.58. She made three purchases of $19.95, $ 27.49, and $ 89.98

How much did she have left?

Add the purchase first… stack them

137.42

Take the total of her purchases and subtract that from the amount she started with $ 317.58

 

180.16

She had $180.16 left!

Estimations-  round to the highest place value of the SMALLEST number.

8.574 + 81.03 + 59.432

First figure out which is the smallest number?

In this case it is 8.574

Round that to its highest place value

8.574 rounded  to the ONES place is 9

so round all the other numbers to the ONES places

and add them

9 + 81 + 59

You can stack them and add normally

9 + 81 + 59 = 149

76.061 – 3.211

when you estimate you get 76  - 3= 73

When you actually add them you arrived at

76.061
-3.211

72.850

Which we write as 72.85

What happens with

(75.004 – 1.32) + ( 41.13 – 2.891)

First take the difference of each set of ( )

then add the differences

73.684 + 38.239 = 111.923