Learning Objectives
- Solve addition and subtraction problems with larger numbers
- Use mental math tricks to add and subtract quickly
- Solve fun puzzles and riddles using addition and subtraction
- Apply addition and subtraction in real-life situations like shopping
Key Concepts
Mental Math for Addition
You can add numbers quickly in your head using smart tricks. To add 9, first add 10 and then subtract 1. For example, 36 + 9 = 36 + 10 - 1 = 45. To add 99, add 100 and subtract 1. For example, 250 + 99 = 250 + 100 - 1 = 349. These tricks make you faster!
Mental Math for Subtraction
To subtract 9, first subtract 10 and then add 1. For example, 53 - 9 = 53 - 10 + 1 = 44. To subtract 99, subtract 100 and add 1. For example, 345 - 99 = 345 - 100 + 1 = 246. Practice these tricks every day!
Number Puzzles
Number puzzles are fun ways to practice addition and subtraction. In a magic square, all rows, columns, and diagonals add up to the same number. In a number wall, each brick shows the sum of the two bricks below it. These puzzles make math exciting!
Shopping Problems
When you go shopping, you use addition to find the total cost and subtraction to find the change. If you buy a toy for Rs 45 and a book for Rs 30, the total is 45 + 30 = Rs 75. If you give Rs 100, your change is 100 - 75 = Rs 25.
Important Terms
- Mental Math: Doing calculations in your head without writing
- Total: The answer when you add all amounts together
- Change: The money you get back after paying more than the cost
- Magic Square: A grid where all rows, columns, and diagonals add up to the same number
- Number Wall: A puzzle where each brick is the sum of the two bricks below
Quick Revision
- To add 9: add 10, subtract 1
- To add 99: add 100, subtract 1
- To subtract 9: subtract 10, add 1
- To subtract 99: subtract 100, add 1
- Total cost = Price of item 1 + Price of item 2 + ...
- Change = Money given - Total cost
- Practice mental math to become faster at calculations