Add and Subtract Whole Numbers and Decimals

The number to be subtracted is the subtrahend and the other number is the minuend

Look at the digits in the ones place. If subtracting these digits gives a negative number, trade 1 ten for 10 ones

Look at the digits in the tens place. If subtracting these digits gives a negative number, trade 1 hundred for 10 tens. Subtract in each column

To subtract decimals, first line up the decimal points. Subtract the decimals first and then the whole numbers. Regroup if the difference is negative

1 hundredth = 10 tenths; 1 tenth = 10 ones

Left to Right Subtraction Method can be used to subtract two numbers

Write the subtrahend as Hundreds + Tens + Ones. Subtract the hundreds, then the tens and finally the ones

Compensation method: Add/Subtract the same number to both numbers in the problem, the answer is the same. Use this rule to change the subtrahend in the problem to a number that has 0 in the ones place. Make the same change to the minuend. Then subtract

To subtract decimals, subtract the ones, then the tenths, and finally the hundredths. Regroup if the difference is negative

1 hundredth = 10 tenths; 1 tenth = 10 ones

We can use models to add numbers with regrouping

Step 1: Add ones. If the sum is greater than 10, regroup. 10 ones = 1 tens
Step 2: Add tens. If the sum is greater than 10, regroup. 10 tens = 1 hundreds
Step 3: Add hundreds. If the sum is greater than 10, regroup. 10 hundreds = 1 thousands. Similarly add thousands

When the numbers are close to a ten or hundred you can use compensation method to simplify addition

If we add a number to one addend and subtract the same number from the other addend, the sum remains the same. For example – To add 29 and 31, add 1 to 29 to make it 30 and subtract 1 from 31. The sum of 29 and 31 is 30 + 30 = 60

There are different methods we can use to add. One of these is called the partial-sums method

For example, add 245 and 187 using partial-sums method. Steps to follow:
Step 1: Add the 100s
200 + 100 = 300
Step 2: Add the 10s
40 + 80 = 120
Step 3: Add the 1s
6 + 7 = 12
Step 4: Add the sums we just found (the partial sums)
300 + 120 + 12 = 432

To add decimals, first line up the decimal points. Add the ones, then the tenths, and finally the hundredths separately. Add the partial sums

Add decimals the same way you add whole numbers. First line up the decimal points. Then add the decimals from right to left

Regroup if the sum exceeds 10. 1 hundredth = 10 tenths; 1 tenth = 10 ones

Add the whole numbers. Regroup if the sum exceeds 10

1 ten = 10 ones; 1 hundred = 10 tens; 1 thousand = 10 hundreds