3rd Class Mathematics Subtraction Subtraction

Subtraction

Category : 3rd Class

LEARNING OBJECTIVES

This lesson will help you to:

  • Understand the concept of subtraction using a 10 x 10 grid.
  • Subtract using 2 digit numbers.
  • Subtract using 3 digit numbers.
  • Apply subtraction to real life situations.

 

Real life Examples

  • Elevator is a real life example of addition and subtraction. The ground floor is considered to be 0.
  • Subtraction helps in calculating the amount left in bank account after debits.

 

AMAZING FACTS

  • Subtract is formed by two words “sub” and “tract”. “Sub” means “below” and “tract” means “to pull away”.
  • When we subtract zero from a particular number (or digit of a number) we get the number (or the digit) itself. For example: 413-100=313

 

QUICK CONCEPT REVIEW

Subtraction is taking away a certain number of objects from a bigger set of objects.

 

MORE ABOUT SUBRTACTION

  • Subtraction is one of the basic four operations.
  • It is denoted by the symbol “-“. For example: 12 subtracted from 45 can be written as 45-12.
  • The number of items left after subtraction is called “difference”.
  • A 10 x 10 number grid is a helpful tool to subtract 2-digit numbers.
  • Some words that denote addition are "minus", "take away" and "left",
  • Addition can be done in different ways
  • Counting in tens: 47- 34 = 47 - 10 -10-10-4
  • Place value: 56 - 13

6 – 3 = 3

50 - 10 = 40

40 + 3 = 43

 

HISTORICAL PREVIESW

  • The plus and minus symbols were in use before they appeared in print. For example, they were painted on barrels to indicate whether or not the barrels were full.
  • To make subtraction easier it is important to regroup the numbers.

For example: 781 - 676

Subtract the ones = 11 - 6 = 5

Subtract the tens = 70-70=0

Subtract the hundreds = 700 - 600 = 100

100 + 5 = 105

 

MISCONCEPT/CONCEPT

  • Misconcept: Subtraction is commutative.
  • Concept: Subtraction is not commutative. For example:

18-13 is not equal to 13-18

 

PLAY TIME:

  • Pick up a 3 digit number. Mix the digits of the number and form a new 3-digit number. Subtract the smaller number from the bigger number.

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