Numbers 100 to 200 Chapter Notes | General Mathematics for Primary 2 PDF Download

Introduction

Number Names

Three-digit numbers are made up of digits from 0 to 9 placed in the hundreds, tens, and ones positions.

To write the number name:

• First, say the digit in the hundreds place, followed by the word "hundred." For example, for 139, "one hundred" is written first. 

• Then, write the next numbers.

Example:
The number 139 is written as "one hundred thirty-nine."
Here, "one hundred" represents the hundreds place, and "thirty-nine" represents the tens and ones places combined.

On Abacus 139 is shown as:

Face Value and Place Value

• Each digit in a number has a face value and a place value.
• Face Value: The face value is the digit itself and remains unchanged.
• Place Value: The place value depends on the digit and its position (hundreds, tens, or ones).
• Place value changes if the digit’s position changes.
• A digit has one face value but can have different place values in various numbers.

Expanded Form

• Expanded form shows a number as the sum of the place values of its digits.
• Break the number into hundreds, tens, and ones parts.
• Write each part and add them.
• For three-digit numbers, it’s written as: hundreds + tens + ones.
• Skip zero in a place unless it affects the number.
• Example: Writing 8374 in expanded form.

Short Form

• Short form is the usual way of writing a number with digits.
• From an expanded number, place each digit in its correct position (hundreds, tens, ones).
• Use the face value of each digit in the right place value column.
• Combine the digits to form the number.
• Write 0 for a zero place value, unless it’s the leading digit.

Before, After and Between

• Before: The number just before is one less, called the predecessor.
• Find the predecessor by subtracting 1.
• After: The number just after is one more, called the successor.
• Find the successor by adding 1.
• Between: The number between two numbers is in the middle.
• For consecutive numbers, the number between is one more than the smaller or one less than the larger.

Example: On a number line:

• 151 is before 152 (152 − 1 = 151).
• 159 is after 158 (158 + 1 = 159).
• 155 is between 154 and 156.

Comparing Numbers

• Compare numbers by checking the number of digits first.
• A number with more digits is always bigger.
• For same-digit numbers, compare digits from the leftmost one.
• If leftmost digits are the same, move to the next digit (e.g., tens if hundreds are equal).
• Keep comparing until a difference is found, then use <, >, or =.

Ordering of Numbers

• Ascending Order: Arrange from smallest to greatest.
• Descending Order: Arrange from greatest to smallest.
• Compare numbers using comparison rules to order them.
• Start with the smallest or largest number, then order the rest.
• Use < or > signs to help find the correct order.

Word Problems

• Word problems involve using numbers to solve real-life situations.
• Read the problem carefully to understand what is being asked.
• Identify the numbers given and what needs to be compared or calculated.
• Use comparison skills (e.g., greater than, less than) to find the solution.
• Write a clear answer based on the comparison or calculation.

Example: Simmi counted 132 red flowers, and Aarohi counted 128 yellow flowers in a park. To find who counted more:

• Compare 132 and 128.
• Both are 3-digit numbers; hundreds are 1 (same), tens are 3 and 2 (3 > 2).
• Since 132 > 128, Simmi counted more flowers.