Maths

Mental Maths Tricks

Class 4

🎯 Learning Objectives

📖 Let Us Begin!

Mental maths means doing calculations in your head -- without writing anything down. It is like a superpower for numbers. The more you practise, the faster you get.

Today you will learn simple tricks that will help you solve problems quickly. Ready? Let us go!

Trick 1: Multiply by 10 -- Just Add a Zero

To multiply any number by 10, simply add one zero at the end.

Example
Examples

7 x 10 = 70 | 23 x 10 = 230 | 156 x 10 = 1560

Trick 2: Multiply by 100 -- Add Two Zeros

To multiply any number by 100, add two zeros at the end.

Example
Examples

5 x 100 = 500 | 34 x 100 = 3400 | 120 x 100 = 12000

Trick 3: Multiply by 5 -- Multiply by 10, Then Halve

Multiplying by 5 is easy: first multiply by 10 (add a zero), then divide by 2 (take half).

Example
Examples

14 x 5: Step 1: 14 x 10 = 140. Step 2: 140 / 2 = 70.

36 x 5: Step 1: 36 x 10 = 360. Step 2: 360 / 2 = 180.

48 x 5: Step 1: 48 x 10 = 480. Step 2: 480 / 2 = 240.

Trick 4: Add 9 -- Add 10, Then Subtract 1

Adding 9 is the same as adding 10 and then taking away 1.

Example
Examples

45 + 9: 45 + 10 = 55, then 55 - 1 = 54.

78 + 9: 78 + 10 = 88, then 88 - 1 = 87.

Trick 5: Subtract 9 -- Subtract 10, Then Add 1

Subtracting 9 is the same as subtracting 10 and then adding 1 back.

Example
Examples

63 - 9: 63 - 10 = 53, then 53 + 1 = 54.

82 - 9: 82 - 10 = 72, then 72 + 1 = 73.

Trick 6: Doubling and Halving

Doubling means multiplying by 2. Halving means dividing by 2. These are useful building blocks.

Example
Examples

Double 35 = 70 | Double 120 = 240 | Double 450 = 900

Half of 64 = 32 | Half of 150 = 75 | Half of 500 = 250

Tip: To multiply by 4, double twice. Example: 13 x 4 = double 13 = 26, double 26 = 52.

Trick 7: Adding Near-100 Numbers

To add 99, add 100 and subtract 1. To add 98, add 100 and subtract 2.

Example
Examples

250 + 99: 250 + 100 = 350, then 350 - 1 = 349.

175 + 98: 175 + 100 = 275, then 275 - 2 = 273.

460 + 97: 460 + 100 = 560, then 560 - 3 = 557.

📝 Key Words

WordMeaning
Mental MathsDoing calculations in your head without writing them down.
DoublingMultiplying a number by 2.
HalvingDividing a number by 2.
ShortcutA quicker way to solve a problem.
⭐ Key Points to Remember
🎨 Speed Challenge -- Beat the Clock!

Ask a friend or parent to time you. Try to solve all 10 problems in under 2 minutes. Write only the answers.

No.ProblemAnswer
125 x 10
214 x 5
356 + 9
4100 - 9
5Double 65
6Half of 300
7450 + 99
838 x 5
972 - 9
1011 x 100

My time: minutes. I got out of 10 correct.

Want to use this as a worksheet? Switch to the A4 printable view.

Mathematics -- Class 4

Topic: Mental Maths Tricks
Name: ____________________________Class: 4Date: ________________
Learning Objectives
Let Us Begin!

Mental maths means doing calculations in your head -- without writing anything down. It is like a superpower for numbers. The more you practise, the faster you get.

Today you will learn simple tricks that will help you solve problems quickly. Ready? Let us go!

Trick 1: Multiply by 10 -- Just Add a Zero

To multiply any number by 10, simply add one zero at the end.

Examples

7 x 10 = 70 | 23 x 10 = 230 | 156 x 10 = 1560

Trick 2: Multiply by 100 -- Add Two Zeros

To multiply any number by 100, add two zeros at the end.

Examples

5 x 100 = 500 | 34 x 100 = 3400 | 120 x 100 = 12000

Trick 3: Multiply by 5 -- Multiply by 10, Then Halve

Multiplying by 5 is easy: first multiply by 10 (add a zero), then divide by 2 (take half).

Examples

14 x 5: Step 1: 14 x 10 = 140. Step 2: 140 / 2 = 70.

36 x 5: Step 1: 36 x 10 = 360. Step 2: 360 / 2 = 180.

48 x 5: Step 1: 48 x 10 = 480. Step 2: 480 / 2 = 240.

Trick 4: Add 9 -- Add 10, Then Subtract 1

Adding 9 is the same as adding 10 and then taking away 1.

Examples

45 + 9: 45 + 10 = 55, then 55 - 1 = 54.

78 + 9: 78 + 10 = 88, then 88 - 1 = 87.

Trick 5: Subtract 9 -- Subtract 10, Then Add 1

Subtracting 9 is the same as subtracting 10 and then adding 1 back.

Examples

63 - 9: 63 - 10 = 53, then 53 + 1 = 54.

82 - 9: 82 - 10 = 72, then 72 + 1 = 73.

Trick 6: Doubling and Halving

Doubling means multiplying by 2. Halving means dividing by 2. These are useful building blocks.

Examples

Double 35 = 70 | Double 120 = 240 | Double 450 = 900

Half of 64 = 32 | Half of 150 = 75 | Half of 500 = 250

Tip: To multiply by 4, double twice. Example: 13 x 4 = double 13 = 26, double 26 = 52.

Trick 7: Adding Near-100 Numbers

To add 99, add 100 and subtract 1. To add 98, add 100 and subtract 2.

Examples

250 + 99: 250 + 100 = 350, then 350 - 1 = 349.

175 + 98: 175 + 100 = 275, then 275 - 2 = 273.

460 + 97: 460 + 100 = 560, then 560 - 3 = 557.

Key Words
WordMeaning
Mental MathsDoing calculations in your head without writing them down.
DoublingMultiplying a number by 2.
HalvingDividing a number by 2.
ShortcutA quicker way to solve a problem.

Mathematics -- Class 4 (continued)

Topic: Mental Maths Tricks -- Key Points and Practice
Key Points to Remember
Rapid Practice -- Solve in Your Head!

A. Multiply by 10 and 100

  1. 15 x 10 =
  2. 42 x 10 =
  3. 230 x 10 =
  4. 8 x 100 =
  5. 56 x 100 =

B. Multiply by 5

  1. 12 x 5 =
  2. 24 x 5 =
  3. 18 x 5 =
  4. 32 x 5 =
  5. 50 x 5 =

C. Add and Subtract 9

  1. 36 + 9 =
  2. 54 + 9 =
  3. 91 - 9 =
  4. 70 - 9 =
  5. 125 + 9 =

D. Doubling and Halving

  1. Double 45 =
  2. Double 125 =
  3. Half of 90 =
  4. Half of 260 =
  5. Double 350 =

E. Adding Near-100 Numbers

  1. 150 + 99 =
  2. 225 + 99 =
  3. 340 + 98 =
  4. 180 + 97 =
  5. 500 + 99 =

F. Mixed Rapid Fire -- Use Any Trick!

  1. 19 x 10 =
  2. 16 x 5 =
  3. 88 + 9 =
  4. Half of 180 =
  5. 67 - 9 =
  6. 44 x 5 =
  7. Double 75 =
  8. 300 + 99 =
  9. 13 x 100 =
  10. Half of 420 =
Speed Challenge -- Beat the Clock!

Ask a friend or parent to time you. Try to solve all 10 problems in under 2 minutes. Write only the answers.

No.ProblemAnswer
125 x 10
214 x 5
356 + 9
4100 - 9
5Double 65
6Half of 300
7450 + 99
838 x 5
972 - 9
1011 x 100

My time: minutes. I got out of 10 correct.