Two Digit Addition

Iván Cepero Barmón

Introduction

Addition is a mathematical operation that represents the total amount of objects together in a collection. It is signified by the plus sign (+).

Addition follows several important patterns. The most important patterns are:

It is commutative, meaning that order does not matter.

And it is associative, meaning that when one adds more than two numbers, order in which addition is performed does not matter.

3 + 2 = 2 + 3

(4 + 1) + 5 = 4 + (1 + 5)

Previous Concepts

Student must know to count until 100

Student must know the place values

Student must know one digit addition

Adding 10 in Our Heads

When we add ten, the only change is the tens.

To learn that, the student have to by tens and they will see that the ones don’t change.

10 – 20 – 30 – 40 – 50 – 60…

Adding ten on a Number Grid

1 2 3 4 5 6 7 8 9 10

11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30

31 32 33 34 35 36 37 38 39 40

41 42 43 44 45 46 47 48 49 50

51 52 53 54 55 56 57 58 59 60

61 62 63 64 65 66 67 68 69 70

71 72 73 74 75 76 77 78 79 80

81 82 83 84 85 86 87 88 89 90

91 92 93 94 95 96 97 98 99 100

67 + 10 = ?

1. We find the number in the number grid.

2. We chose the box below.

Patterns When Adding ten

Only change the tens adding one more.

27 + 10 = 37

34 + 10 = 44

Adding Multiples of 10 on a Number Grid

The first rule is the same but the second no.

We go down as many boxes as tens there are.

1 2 3 4 5 6 7 8 9 10

11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30

31 32 33 34 35 36 37 38 39 40

41 42 43 44 45 46 47 48 49 50

51 52 53 54 55 56 57 58 59 60

61 62 63 64 65 66 67 68 69 70

71 72 73 74 75 76 77 78 79 80

81 82 83 84 85 86 87 88 89 90

91 92 93 94 95 96 97 98 99 100

51 + 20 = ?71

Adding Multiples of 10

We can use the head and the fingers.

We only add tens, the ones are the same.

We have the bigger multiple of ten in the head and we count with the finger the other multiple.

32 + 40 = ?

HEADFINGERS

72

Two Digit Plus One Digit

It is very important to know line them. The way to line them is putting the numbers from right to left.

When there isn´t digit in tens we know that it is “0”

First, we add the ones and then the tens

23+ 4

23+04

Two Digit Plus Two Digit

It is the same process that two digit plus one digit.

First we put the number from right to left

Then we add first the ones and the tens later

2 3+4 6 6 9

1st2nd

Regrouping

We must remind student that ten ones are one ten

When the sum of the ones is greater than nine means that there is a ten and it must be regrouped.

The regrouping is done regrouping the ten to the tens column and add them.

3 5+ 2 7 12

1 3 5+2 7 6 2

conclusion

Learn to add numbers is a vital mathematical ability. Students

must know how to add in order to develop their knowledge of

mathematics.

It is important not only for that, it is also essential for daily life.