Math 6A ( Periods 2 % 5)

Adding and Subtracting Decimals  2-4

Decimals may be added or subtracted using the same rules as whole numbers

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

Annex zeros to get the same number of decimal places and then add or subtract as if the numbers were whole numbers.

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

Add 6.47 + 340.8 + 73.523

STEP 1	STEP 2	STEP 3
6.47	6.470	6.470
340.8	340.800	340.800
+   73.523	+  73.523	+  73.523
	420 793	420.793

The use of rounded numbers to get an approximate answer is called estimation. We use estimates to check actual answers. Use estimates as a habit to check if your answer is reasonable.

To find an estimate, first round the highest place value of the smallest number, then compare.

Add 8.574 + 81.03 + 59.432. Then estimate to check your answer.  What is the highest place value of the smallest number?          9 + 81 + 59  = 149