There are a number of useful mental strategies for addition. Some examples are given below.
Add tens, then add units, then add together.
Split up number to be added into tens and units and add separately.
Round up to the nearest 10, then subtract.
but 30 is 3 too much so subtract 3
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
Add the units. 2 + 9 = 11. Carry the 10 to the next column.
Add the tens. 3 + 8 plus the 1 from the previous column = 12. Carry the 10 to the next column.
Add the hundreds. Zero + 5, plus the 1 carried from the previous column = 6. This time there are no tens to carry over.
Add the thousands. 3 + 0 = 3