Adding Tens
How to add two-digit numbers (for example 30 + 40).
- First line up the numbers as per the place value (all the tens and the units lined up vertically). Put a line under the last number.
30 40- Add the ones' place numbers. (0 + 0 = 0). Write the zero in the ones' place column.
30 40 0- Add the tens' place digits (3 + 4 = 7) and write the answer below the line in the tens' place column.
30 40 70
Adding Two-Digit Numbers
How to add two two-digit numbers (for example 54 + 42).
- First line up the numbers as per the place value (all the tens and the units lined up vertically). Put a line under the last number.
54 42- Add the numbers in the ones' place digits (4 + 2 = 6).
54 42 6- Add the the tens' place digits(5 + 4 = 9) and write the answer below the line in tens' place column.
54 42 96
Adding Three One-Digit Numbers
Adding three numbers (for example 5 + 3 + 9) involves two steps.
- First line up the numbers as per the place value (all the tens and the units lined up vertically). Put a line under the last number.
- Add the first two digits. (5 + 3 = 8). Hold '8' in your mind.
- Add the other digit to this sum. (8 + 9 = 17).
Adding Hundreds
How to add three-digit numbers (for example 400 + 300).
- First line up the numbers as per the place value (all the hundreds,tens and the ones lined up vertically). Put a line under the last number.
400 300- Add the numbers in the ones' place digits. (0 + 0 = 0) and write the answer below the line in the ones' place column.
400 300 0- Add the tens' place numbers (0 + 0 = 0) and place the answer below the line and to the tens' place column
400 300 00- Add the digits in the hundreds' place column (4+ 3 = 7) and write the answer below the line in the hundreds' place column.
400 300 700
The addition facts for 0, 1 and 2 are in the following table.
ZERO | ||||
0+0=0 | 0+1=1 | 0+2=2 | 0+3=3 | 0+4=4 |
ONE | ||||
1+1=2 | 1+2=3 | 1+3=4 | 1+4=5 | 1+5=6 |
TWO | ||||
2+2=4 | 2+3=5 | 2+4=6 | 2+5=7 | 2+6=8 |
When 0 is added to a second digit the answer is the second digit. (e.g. 0 + 6 = 6)
Adding 1 to any number is like counting up by 1.
Adding 2 to any number is like counting up by 2.
Mentally Adding Two-Digit Numbers
How to mentally add two two-digit numbers.
To add 73 and 34
- First add the digits in the ones' place(3 + 4)=7.
- Add digits in the tens' place(7 + 3) = 10.
- If the sum of ones's place numbers is single digit number then write the answer 107.
To add 65 and 87
- First add the digits in the ones' place(5 + 7)=12
- Add digits in the tens' place(6 + 8)=14
- If the sum of ones's place numbers is two-digit number then do the following
- Decrease the sum of ones's place by 10(12-10= 2)
- Increase the sum of tens' place by 1(14 + 1=15)
- Write the sums of tens and ones' place together to get the answer of 152
How to add two two-digit numbers (for example 35 + 78) with paper and pencil.
- First line up the numbers as per the place value (all the tens and the units lined up vertically). Put a line under the last number.
35 78- Add the numbers in the ones' place. (5 + 8 = 13). This sum is a two-digit number so write 1 above the tens' place column and write the 3 below the line in the ones' place column.
1 35 78 3- Add the digits in the tens' place column (1 + 3 + 7 = 11) and write the answer below the line in the tens' place column.
1 35 78 113
Here are the steps to add two-digit numbers (for example 67 + 89) using calculator
- Type the first number 67 by presing the 6 button and the 7 button
- Press + button
- Type the second number 89 by pressing the 8 button and the 9 button
- Press the = button to get the answer.
Estimating a sum by rounding
How to Estimate a sum by rounding.
- Round each two-digit number
- Add the rounded numbers to get the best estimate.
For example, estimate the following sums:
46 + 31, 64 + 25, and 45 + 34
46 + 31 = 50 + 30 = 80
64 + 25 = 60 + 30 = 90
45 + 34 = 50 + 30 = 80