Numbers - Notes | Study Mathematics Olympiad for Class 1 - Class 1

Introduction
Zero

• Zero is the smallest counting number. It is represented as 0.
• The image below shows a jar with two balls – black and white
• Now if you remove the two balls, the jar contains 0 balls—
  

Numbers from 0 to 9 are one-digit numbers. 

A number line can be defined as a straight line with numbers placed at equal distance along its length.

• The value of each digit in a number is known as place value.
• Starting from right, the first place is units or ones (O) and the second place is tens (T).

Example: The place value of the two-digit number 13 will be as follows:

• Numbers from 10 to 99 are two-digit numbers.
  
• Here are some examples for two-digit numbers.
• How to get the number 18?
  
• What number do you get when 3 tens is added to 4 ones?
  
• What number do you get when 5 tens is added to 1 one?
  
• What number do you get when 7 tens is added to 2 ones?
• What number do you get when 8 tens is added to 6 ones?
  
• What number do you get when 9 tens is added to 8 ones?
  
• See the following examples.

Given that
 
(a)
(b)
(c)

(d)
(e)
(f)
(g)
(h)

Greater than

• Greater than Which number is greater: 7 or 10?
• We can identify the greater number using a number line.
  
• 10 lies on the right side of 7, so 10 is greater than 7 and we write it as 10 > 7.

• Which number is smaller: 34 or 53?
• We compare the numbers using a number line.
  
• 34 lies on the left side of 53, so 34 is smaller than 53 and we write it as 34 < 53.

• If the two numbers given are same, we say that the numbers are equal.
• We can say that 7 is equal to 7 and write it as 7 = 7

Example: Are the numbers 19 and 91 equal?

The given numbers are 19 - Nineteen and 91 - Ninety-one. They are not same. So, 19 and 91 are not equal.

9, 8, 7, 6, 5, 4, 3, 2, 1, 0 is the backward order of one-digit numbers.

99, 98, 97, 96, 95, 94, 93, 92, 91, 90, 89, _______, 10 is the reverse order of two-digit numbers.

• Ascending order means arrangement of numbers from small to big.
• Descending order means arrangement of numbers from big to small.
  

Examples:

• Arrange the given numbers in ascending order: 54, 28, 47, 87, 18, 64
• Arrange the numbers from the smallest to the biggest or largest.
  So, the order is 87, 64, 54, 47, 28, and 18.
• Arrange the numbers 45, 12, 56, 84 in descending order.
  
• Arrange the numbers from the biggest or largest to the smallest.

  So, the order is 84, 56, 45, 12.

Just before, Just after, and In-between

• If the numbers are 13, 14, and 15,
• 13 comes just before 14.
• 15 comes just after 14.
• 14 lies in between 13 and 15.

Numbers obtained by adding the same number.
Example:

• 2, 4, 6, 8, 10 are the numbers we get by skip count of 2.
  
• 3,6,9,12,15 are the numbers we get by skip count of 3.
  
• 4, 8, 12, 16, 20 are the numbers we get by skip count of 4.
  
• 5, 10, 15, 20, 25 are the numbers we get by skip count of 5.
  
• 10, 20, 30, 40, 50 are the numbers we get by skip count of 10.