## The numbers addition to perform:

77 + 92 + 120 + 121

#### Method used below: column adding, from right to left (traditional).

### Stack the numbers on top of each other.

#### The ones digits line up in the first column from the right.

#### The tens digits line up in the next column to the left.

#### And so on...

## Add column by column; start from the column on the right.

### Add the digits in the ones column:

#### 7 + 2 + 0 + 1 = 10

#### The sum is a two-digit number: 10.

#### 0 is the ones digit.

Write it down at the base of the ones column.

#### 1 is the tens digit.

Carry it over to the tens column.

Write the digit above that column.

Add it with the rest of the digits in that column.

### Add the digits in the tens column:

#### 7 + 9 + 2 + 2 + 1 = 21

#### How did we add the digits? Explanation below.

#### Group the ones together in order to make tens:

#### 7 + 9 + 2 + 2 + 1 =

#### 7 + 9 + 2 + 2 + 1 =

#### 7 + (9 + 1) + 2 + 2 =

#### 7 + 10 + 2 + 2 =

#### 7 + 10 + 2 + 2 =

#### 7 + 10 + 4 =

#### 7 + 10 + 4 =

#### 7 + 10 + 3 + 1 =

#### 7 + 10 + 3 + 1 =

#### (7 + 3) + 10 + 1 =

#### 10 + 10 + 1 =

#### 10 + 10 + 1 =

#### 20 + 1 =

#### 21

#### Change the order in which the numbers are added, the sum stays the same.

Break some number(s) into component parts, the sum stays the same.

#### The sum is a two-digit number: 21.

#### 1 is the tens digit.

Write it down at the base of the tens column.

#### 2 is the hundreds digit.

Carry it over to the hundreds column.

Write the digit above that column.

Add it with the rest of the digits in that column.

### Add the digits in the hundreds column:

#### 1 + 1 + 2 = 4

#### 4 is the hundreds digit.

Write it down at the base of the hundreds column.

## Answer: