Addition

There are a number of useful mental strategies for addition.  Some examples are given below.

Mental Methods

Example:

add-calculation1

Method 1

Add tens, then add units, then add together.

add-method1a

Method 2

Split up number to be added into tens and units and add separately.

add-method2a

add-method2b

Method 3

Round up to the nearest 10, then subtract.

add-method3a

 

but 30 is 3 too much so subtract 3

add-method3b

Written Method

When adding numbers, ensure that the numbers are lined up according to place value.  Start at right hand side, write down units, carry tens.

Example – add 3032 and 589

Step 1

Add the units.  2 + 9 = 11.  Carry the 10 to the next column.

add-written1

Step 2

Add the tens.  3 + 8 plus the 1 from the previous column = 12.  Carry the 10 to the next column.

add-written2

Step 3

Add the hundreds.  Zero + 5, plus the 1 carried from the previous column = 6.  This time there are no tens to carry over.

add-written3

Step 4

Add the thousands.  3 + 0 = 3

add-written4

 

 

 

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