## The operation to perform:

- 68 - 90

### Add the numbers as if they were positive.

#### But at the end attach a minus sign in front of the result.

#### 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.

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

### Add the digits in the ones column:

#### 8 + 0 = 8

#### 8 is the ones digit.

Write it down at the base of the ones column.

### Add the digits in the tens column:

#### 6 + 9 = 15

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

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

#### 6 + 9 =

#### 6 + 9 =

#### 1 + 5 + 9 =

#### 1 + 5 + 9 =

#### (1 + 9) + 5 =

#### 10 + 5 =

#### 15

#### 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: 15.

#### 5 is the tens digit.

Write it down at the base of the tens column.

#### 1 is the hundreds digit.

Write it down at the base, next to the tens digit.

### Addition result:

#### 68 + 90 = 158

## Answer:

- 68 - 90 = - 158