2nd Class Mathematics Addition and Subtraction

Addition and Subtraction

Synopsis

ADDITION:  

• Taking things (or numbers) together is called addition. + is the symbol for addition.

• When 0 is added to a number, the sum is the same number. e.g., 6 + 0 = 6
• When 1 is added to a number, the sum is the next number. g., 4 + 1 = 5

• Regrouping: Writing a number in different ways is called regrouping.

e.g.,          16 ones = 1 ten 6 ones

25 tens = 2 hundreds 5 tens

• Addition of two number with carry:

When two numbers in ones place are added, the sum may be greater than 9.   

Then regroup the sum as tens and ones.                                  

e.g., Add 276 and 389.                              
                              

6 + 9 = 15       

15 = 1 ten 5 ones

Write the ones under the ones place and carry the number in tens to the tens place.    

Then add the numbers in tens place along with the carry. Write the sum under tens place if it is less than or equal to 9.    

If the sum of tens is greater than 9, again regroup the tens as hundreds and tens. 16 tens = 1 hundred 6 tens.

Write the tens in tens place and carry the hundreds to hundreds place. Add the numbers in hundreds place along with the carry and write the sum.            

So, 276 + 389 = 665.                                                 

Subtraction:

• Taking away some things (or numbers) to find how much is remaining is called subtraction. - is the symbol for subtraction.

• When 0 is subtracted from a number, the difference is the same number.

e.g., 6 - 0 = 6

• When 1 is subtracted from a number, the difference is its previous number.

e.g, 9 - 1 = 8   

Subtraction of two numbers (Without borrow)

• Two 1 - digit numbers: Subtract the numbers and write the difference.

e.g.,         Subtract 3 from 8.

8 - 3 = 5 (Horizontal subtraction)

         8

-3       
______ (Vertical subtraction)

                5

               ______

• Two 2 - digit numbers: (i) First subtract the ones and (ii) then subtract the tens.

e.g.,         Find 67 - 42.  

          (i)                        (ii)   

• Two 3 - digit numbers: (i) First subtract the ones, (ii) then tens and (iii) then hundreds.

e.g.,    Subtract 103 from 216.  

(i)                   (ii)

(iii)  

• Subtraction with borrow:

When the subtrahend is larger than the minuend, subtraction cannot be done. Then we borrow from the next place.

e.g., 1: Subtract 38 from 54.

We cannot subtract 8 from 4. So we borrow 1 from the tens place       

In the ones place, 1 ten is added to 4 ones. So it becomes 14 ones. Now subtract 8 from 14 and write the difference 6 in ones place.           

In the tens place, the minuend becomes 5-1=4. Now subtract 3 from 4 and write the difference under tens.                          

So, 54 - 38 = 16.

e.g., 2: Subtract 457 from 634.

     (i)                  (ii)

(iii)  

So, 634 - 457 = 177.

• Every addition sentence has two subtraction facts.

e.g., 7 + 4 = 11 \[\to \] a) 11 - 7 = 4 and b) 11 - 4 = 7

• Every subtraction sentence has two addition facts.

e.g., 16 - 3 = 13 \[\to \] (a) 13 + 3 = 16 and (b) 3 +   

13 = 16