Lesson 1, Topic 3
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# Counting Numbers

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Counting numbers are sets of numbers that we use to learn how to count. They are for counting and measuring in our everyday life e.g the quantity of salt to be used for cooking, the quantity of sugar to be used in tea, and the speedometer of a vehicle.

### Examples of Counting Numbers:

1. Natural Numbers
2. Prime Numbers
3. Even Numbers
4. Odd Numbers

1. Natural  Numbers: These are whole numbers greater than zero e.g 1, 2, 3, 4, 5, 6, 7 …

2. Prime Numbers: These are natural numbers which have no factor other than 1 and themselves. In other words, they can be divided only by themselves or 1, e.g 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31 ….

3. Even Numbers: The set of all-natural number which is divisible by 2. It is denoted by E. where E = {2, 4, 6, 8, 10, … .$$\scriptsize \infty$$}

4. Odd Numbers: The set of all natural numbers which are not divisible by 2 are called odd numbers, in other words, the natural numbers which are not even numbers are odd numbers. It is denoted by O. i.e. O = {1, 3, 5, 7 …. $$\scriptsize \infty$$}

Note:
$$\scriptsize \infty$$means infinity. Infinity is the idea of something that has no end.

### Example 1

Write down all natural numbers between 30 and 40.

Solution

31, 32, 33, 34, 35, 36, 37, 38, 39.

Note:
30 and 40 are not inclusive because the question says “between” 30 and 40.

### Example 2

Write all the prime numbers from 11 to 31.

Solution

11, 13, 17, 19, 23, 29, 31

### Example 3

List all the odd numbers between 50 and 70.

Solution

50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70

Ans = 51, 53, 55, 57, 59, 61, 63, 65, 67, 69.

### Example 4

List the first five even numbers from 110.

Solution

110 111 112 113 114 115 116 117 118

Ans = 110, 112, 114, 116, 118.

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