# 1st Class Mathematics Number Sense Number Sense

## Number Sense

Category : 1st Class

LEARNING OBJECTIVES

• understand numbers from 0 to 99.
• understand one digit and 2-digit numbers.
• understand missing numbers.
• understand the numbers coming after, before and in-between the given numbers.
• learn about place value of numbers.
• learn how to write number name.
• compare numbers.
• understand backward and skip counting.

QUICK CONCEPT REVIEW

ZERO

Zero is the first number in the counting and it is written as 0. The number zero represents having no value. This can be understand by following example:

 1 Suppose there are 5 birds sitting on the branch of the tree. 2 Out of 5 birds, 2 fly away, so now 3 birds are sitting on the branch of the tree. 3 The remaining birds also fly away and now there are zero birds on the branch.

Numbers from 0 to 9 are called one digit numbers. Numbers from 10 to 99 are called two digit numbers.

Amazing Facts

0 is the least number, 9 is the largest 1 digit number and 10 is the smallest 2 digit number.

Historical Preview

Zero is the only number which cannot be represented in Roman.

Zero was discovered by an Indian Mathematician named Aryabhatta.

NUMBER LINE

Arrangement of numbers from left to right in a line in increasing order is called number line. For example numbers from 0 to 10 are shown in the number line as following.

Number line is useful in addition and subtraction and also tells the relation between the numbers. We will learn about number line in higher classes.

PLACE VALUE OF A NUMBER

In any two digit number first number from right is called ones and second number from right is called tens. For example:

$\to$  35 and 5 ones and 3 tens

BUILDING NUMBERS

Building numbers from 11 to 20: Addition method is used for building of numbers for example. When we add 1 to 10 then it will form 11. Similarly, 2 is added in 10 to get number 12.

Building Numbers From 21 to 50: Now, let us take some examples to build numbers from 21 to 50.

When we add 1 to 20 then it will form 21.

Let us understand with an example

BEFORE AFTER AND BETWEEN

One more than a number corner after it.

One less than a number comes before it.

For example:

COMPARING NUMBERS

How will you compare two numbers?

Greater than (>), less than (<) or equal to (=) signs are used to compare numbers.

For example:

1.

Here 3 is less than 7.

2.

8 is more than 6.

ORDERING NUMBERS

Numbers, when arranged from the smallest to the largest are said to be in ascending or increasing order.

For example: --

Numbers  can be arranged in ascending or increasing number as following.

$\to$from the lowest step to the highest step

Numbers when arranged from the largest to the smallest are said to be in descending or decreasing order.

Example: 

-->  from the highest step to the lowest step

BACKWARD COUNTING

In backward counting the numbers are written in reverse order.

For example

1. 50 49   48   47   46   45   44   43   42   41

40   39   38   37   36   35   34   33   32   31

30   29   28

1. 10 9    8   7  6   5   4    3    2    1

SKIP COUNTING

In skip counting, value of the numbers increase uniformly

For example:

(a) Skip counting of 2 can be written OS-

2, 4, 6, 8, 10...

(b) Skip counting of 3 can be written OS-

3, 6, 9, 12, 15...

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