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Sep 7 2015

Making mistakes while adding two digit numbers

Knowing when to step back and allow your child to make mistakes  and when to step in can be tricky. I have been allowing my daughter to add incorrectly before I decided to step in and clear up her concepts. In this post, I will be writing down where-all Arpita was making mistakes while adding two digit numbers and how we both dealt with it. 

This is one of the ways addition is being taught in school.

     3 5

 + 4 2



My daughter started adding from either the tens column or the ones column. So long as the problems were not carry over sums, the answer would be correct even when her approach was wrong. Nobody but I knew that she was approaching the problem incorrectly and she was happy with the smilies she got in school. But, I realized that once she will have to deal with carry over problems she will be making mistakes. Also this meant that she was not clear with the concept of tens and ones.

This is how I went about explaining addition to her

Step 1

In school as of now we follow the decimal number system with a base 10.

0, 1, 2, 3, 4, 5, 6, 7, 8, 9 are all called single digits. We can count these numbers on our fingers. These are all single digits, meaning they stand alone with no numbers around them. When we write them they will always come under ones. 

While counting starting from zero, once you reach 10, it can no longer stay in ones place. It will have to move Tens place. Tens place is always on the left of ones.

Easy way to remember is TO

Step 2

So whenever you are asked to do additions in class. For example:

    3 5

+ 4 3



Always write Tens and ones first ie TO starting from very right above the digits and going left. Once you do this first step, you will never go wrong.


     T O

     3  5

 + 4  3



Step 3


Here you have to identify which is the bigger number under ones column. It is 5. 

So we keep 5 on our head. The other number ie. 3, we will show on our fingers.

Now to add we will count after 5. Since we have 3 fingers up. So it will be 6, 7, 8.

So 5+3 will be 8.

Similarly we add 3 and 4 to get 7.

     T O

     3  5

 + 4  3


     7  8


Now that she can easily add both single and double digit number she looks at me beseechingly for a story. This seemed the ideal time to talk to her about Pythagoras and then introduce Tetractys to her.


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