Operation with whole numbers

When adding numbers we add the corresponding digits in their corresponding place values and we start adding from the right side, i.e., from the place value of ones to the next.

We can add numbers horizontally or vertically.

Horizontal Addition

Example

1. $972 + 18 = 990$
2. $23,750 + 250 = 24,000$

Vertical Addition

Example

    4 2 6
  + 3 7 3
  -------
    7 9 9

Subtraction is denoted by the sign (−). It is sometimes called minus. Subtraction is the opposite of addition. Subtraction also means reducing a number from a certain number and the answer that is obtained is called the difference.

Example

    5 0 5
  -   1 3
  -------
    4 9 2

Multiplication means adding repeatedly depending on the number of times given. For example:

$25 \times 6 = 25 + 25 + 25 + 25 + 25 + 25 = 150$

The answer obtained is called the product. The number being multiplied is called the multiplicand and the number used in multiplying is called the multiplier.

Example

      1 2
    ×  4
  -------
     4 8

Division is the same as repeated subtraction. You subtract the divisor from the dividend repeatedly until you get zero. The number of subtractions gives the quotient.

For example:

$27 \div 9 = 3$

Short Division Example

    ______
  9 ) 2 7
        -18
        ----
           9
        - 9
        ----
           0
  Quotient = 3

Sometimes you may be given a question with mixed operations +, -, × and ÷. Use the BODMAS rule:

Example

$12 \div 4 + 3 \times 5 = 3 + 15 = 18$

$14 \times 2 \div 7 - 3 + 6 = 28 \div 7 - 3 + 6 = 4 - 3 + 6 = 7$

BODMAS stands for:

• Brackets
• Orders (powers, roots)
• Division
• Multiplication
• Addition
• Subtraction

Example

In a school library there are 6 shelves each with 30 books.

$6 \times 30 = 180$ books

Example

Juma's mother has a garden with Tomatoes, Cabbages and Water Lemons. There are 4 rows of Tomato each with 30 in it. 6 rows of Cabbages with 25 in each and 3 rows of Water Lemons with 15 in each.

Juma's mother has:

• $4 \times 30 = 120$ Tomatoes
• $6 \times 25 = 150$ Cabbages
• $3 \times 15 = 45$ Water Lemons

Total = $120 + 150 + 45 = 315$ plants

Example

A school shop collects sh 90,000 from customers each day. If sh 380,000 from the collection of 6 days was used to buy books. How much money was left?

A school shop collects $90,000$ per day. 6 days: $90,000 \times 6 = 540,000$

Books cost $380,000$

Left = $540,000 - 380,000 = 160,000$