Lesson 2 : Whole Number Operations.
Key Ideas :
* Add when combining amounts and subtract when finding the difference.
● Align place- value columns when adding or subtracting .
● Always look to the next place-value column to regroup.
● G** Test Tips .
[ Another way to check answers is to round the numbers in a problem and find an
approximate answer.]
Addition and Subtraction .
You use ( addition ) when you need to combine amounts. The answer in an addition problem is
called the ( sum) , or ( total ) . When you are adding , it’s helpful to stack the numbers in a
column . Be sure to line up the place-value columns and than work from right to left , starting
with the ones.
Sometimes the digits in a place- value column add up to 10 or more. When this happens , you
will need to ( regroup ) to the next place value.
Example 1 : Add 40+ 129 + 24 .
1. Align the numbers you want to add on the ones column . Working from right to left, add
the ones column first . Since the ones column totals 13, write the 3 in the ones column
and regroup , or ( carry ) , the 1 ten to the tens columns.
2. Add the tens column , including the regrouped 1 .
3. Then add the hundreds column. Since there is only one value , write the 1 hundred in
the answer.
You ( subtract) when you want to find the ( difference ) between amounts. Write the greater
number on top , and align the amounts on the ones column. You may also need to regroup as
you subtract.
Example 2 : If Sue is 57 and Kathy is 38 , how many years older is Sue ?
1. Find the difference in their ages. Start with the ones column . Since 7 is less than the
number being subtracted ( 8 ) , regroup or ( borrow ) 1 ten from the tens column. Add the
regrouped amount to the ones column. Now subtract 17-8 in the ones column.
2. Regrouping 1 ten from the tens column left 4 tens. Subtract 4-3 and write the result in
the tens column of your answer. Check : 17-8 in the one column .
Sue is 19 years older than Kathy.
1
40
129
Key Ideas :
* Add when combining amounts and subtract when finding the difference.
● Align place- value columns when adding or subtracting .
● Always look to the next place-value column to regroup.
● G** Test Tips .
[ Another way to check answers is to round the numbers in a problem and find an
approximate answer.]
Addition and Subtraction .
You use ( addition ) when you need to combine amounts. The answer in an addition problem is
called the ( sum) , or ( total ) . When you are adding , it’s helpful to stack the numbers in a
column . Be sure to line up the place-value columns and than work from right to left , starting
with the ones.
Sometimes the digits in a place- value column add up to 10 or more. When this happens , you
will need to ( regroup ) to the next place value.
Example 1 : Add 40+ 129 + 24 .
1. Align the numbers you want to add on the ones column . Working from right to left, add
the ones column first . Since the ones column totals 13, write the 3 in the ones column
and regroup , or ( carry ) , the 1 ten to the tens columns.
2. Add the tens column , including the regrouped 1 .
3. Then add the hundreds column. Since there is only one value , write the 1 hundred in
the answer.
You ( subtract) when you want to find the ( difference ) between amounts. Write the greater
number on top , and align the amounts on the ones column. You may also need to regroup as
you subtract.
Example 2 : If Sue is 57 and Kathy is 38 , how many years older is Sue ?
1. Find the difference in their ages. Start with the ones column . Since 7 is less than the
number being subtracted ( 8 ) , regroup or ( borrow ) 1 ten from the tens column. Add the
regrouped amount to the ones column. Now subtract 17-8 in the ones column.
2. Regrouping 1 ten from the tens column left 4 tens. Subtract 4-3 and write the result in
the tens column of your answer. Check : 17-8 in the one column .
Sue is 19 years older than Kathy.
1
40
129
