Table of 20
The Table of 20 is a crucial multiplication table that helps in fast calculation. Learning this table makes solving problems involving multiples of 20 quick and efficient. Understanding the pattern and trick behind the table of 20 makes memorization easier and more accurate.
1. Complete Table of 20 (1 to 10)
Here is the basic multiplication table of 20 from 1 to 10. These are the core values you must memorize first.
- 20 × 1 = 20
- 20 × 2 = 40
- 20 × 3 = 60
- 20 × 4 = 80
- 20 × 5 = 100
- 20 × 6 = 120
- 20 × 7 = 140
- 20 × 8 = 160
- 20 × 9 = 180
- 20 × 10 = 200
2. Extended Table of 20 (11 to 20)
The extended table helps in solving complex problems faster. These values appear frequently in competitive calculations.
- 20 × 11 = 220
- 20 × 12 = 240
- 20 × 13 = 260
- 20 × 14 = 280
- 20 × 15 = 300
- 20 × 16 = 320
- 20 × 17 = 340
- 20 × 18 = 360
- 20 × 19 = 380
- 20 × 20 = 400
3. The Master Trick: ×2 Then Add Zero Method
This is the fastest and most efficient trick to calculate the table of 20 mentally. The method breaks down 20 as 2 × 10, making calculations instant.
3.1 How the Trick Works
The trick uses the fact that 20 = 2 × 10. Therefore, multiplying any number by 20 is the same as multiplying by 2 first, then multiplying by 10.
- Step 1: Multiply the given number by 2 (double it).
- Step 2: Add a zero at the end of the result (multiply by 10).
- Result: You get the answer instantly.
3.2 Formula Representation
The mathematical formula for this trick is:
20 × n = (2 × n) × 10
- n: The number you want to multiply by 20.
- 2 × n: Double the number (multiply by 2).
- × 10: Adding a zero at the end achieves this multiplication.
3.3 Step-by-Step Examples Using the Trick
3.3.1 Example 1: 20 × 7
- Multiply 7 by 2: 7 × 2 = 14
- Add a zero to 14: 140
- Answer: 20 × 7 = 140
3.3.2 Example 2: 20 × 13
- Multiply 13 by 2: 13 × 2 = 26
- Add a zero to 26: 260
- Answer: 20 × 13 = 260
3.3.3 Example 3: 20 × 18
- Multiply 18 by 2: 18 × 2 = 36
- Add a zero to 36: 360
- Answer: 20 × 18 = 360
3.3.4 Example 4: 20 × 25
- Multiply 25 by 2: 25 × 2 = 50
- Add a zero to 50: 500
- Answer: 20 × 25 = 500
3.4 Why This Trick Works
Understanding the logic behind the trick helps in applying it correctly in all situations.
- Place Value System: Adding a zero shifts all digits one place left, multiplying the number by 10.
- Associative Property: Multiplication can be done in any order: (2 × n) × 10 = 2 × (n × 10) = 20 × n.
- Mental Math Speed: Doubling a number is much easier than directly multiplying by 20.
4. Pattern Recognition in Table of 20
Spotting patterns makes memorization easier and helps verify answers quickly during calculations.
4.1 Key Patterns to Observe
- All Products End in 0: Every multiple of 20 always ends with zero because 20 = 2 × 10.
- Even Numbers Only: All results are even numbers since 20 itself is an even number.
- Increment Pattern: Each successive product increases by exactly 20.
- Divisibility by 10: Every result is divisible by both 10 and 20.
- Relationship with Table of 2: The tens and hundreds digits follow the pattern of the table of 2.
4.2 Comparison with Table of 10
Understanding the relationship between tables of 10 and 20 strengthens mental calculation skills.
Key Insight: Any multiple of 20 is exactly double the corresponding multiple of 10.
5. Practice Exercises for Mastery
Regular practice using the trick ensures speed and accuracy. These exercises progress from simple to complex calculations.
5.1 Basic Level Practice (Using the Trick)
Apply the ×2 then add zero method to solve these quickly:
- 20 × 4 = ? (Hint: 4 × 2 = 8, add zero → 80)
- 20 × 6 = ? (Hint: 6 × 2 = 12, add zero → 120)
- 20 × 9 = ? (Hint: 9 × 2 = 18, add zero → 180)
- 20 × 12 = ? (Hint: 12 × 2 = 24, add zero → 240)
5.2 Intermediate Level Practice
These problems require applying the trick to slightly larger numbers:
- 20 × 15 = ? (Hint: 15 × 2 = 30, add zero → 300)
- 20 × 17 = ? (Hint: 17 × 2 = 34, add zero → 340)
- 20 × 19 = ? (Hint: 19 × 2 = 38, add zero → 380)
- 20 × 22 = ? (Hint: 22 × 2 = 44, add zero → 440)
5.3 Advanced Level Practice
Challenge yourself with larger multipliers to build complete mastery:
- 20 × 24 = ? (Hint: 24 × 2 = 48, add zero → 480)
- 20 × 27 = ? (Hint: 27 × 2 = 54, add zero → 540)
- 20 × 30 = ? (Hint: 30 × 2 = 60, add zero → 600)
- 20 × 35 = ? (Hint: 35 × 2 = 70, add zero → 700)
5.4 Reverse Calculation Practice
Finding the multiplier when the product is given tests complete understanding:
- ? × 20 = 140 (Answer: 7, because 140 ÷ 20 = 7)
- ? × 20 = 260 (Answer: 13, because 260 ÷ 20 = 13)
- ? × 20 = 380 (Answer: 19, because 380 ÷ 20 = 19)
- ? × 20 = 500 (Answer: 25, because 500 ÷ 20 = 25)
6. Common Student Mistakes and Trap Alerts
Being aware of typical errors prevents losing marks in competitive situations. These mistakes happen frequently during speed calculations.
6.1 Mistake 1: Forgetting to Add the Zero
- Wrong Approach: 20 × 8 = 16 (only doubled, forgot to add zero)
- Correct Approach: 8 × 2 = 16, then add zero → 160
- Prevention Tip: Always say "double it, then add zero" as two separate steps.
6.2 Mistake 2: Adding Zero Before Doubling
- Wrong Approach: 20 × 7 → 70 × 2 = 140 (correct answer by luck, wrong method)
- Correct Approach: 7 × 2 = 14, then add zero → 140
- Prevention Tip: The sequence matters. Always double first, then add zero.
6.3 Mistake 3: Confusion with Table of 2
- Wrong Approach: Giving the table of 2 answer instead of adding the zero (20 × 5 = 10)
- Correct Approach: 5 × 2 = 10, then add zero → 100
- Prevention Tip: Remember that 20 is ten times 2, not just 2.
6.4 Mistake 4: Incorrect Doubling of Large Numbers
- Example Error: 20 × 18 → 18 × 2 = 32 (wrong), then 320 (wrong)
- Correct Calculation: 18 × 2 = 36, then add zero → 360
- Prevention Tip: Practice the table of 2 up to 30 for strong foundation.
7. Quick Revision Summary
Use this section for last-minute revision before any test or calculation challenge.
7.1 The Golden Trick Formula
20 × n = (n × 2) × 10
- Double the number.
- Add a zero at the end.
- This works for any positive number.
7.2 Must-Remember Milestones
- 20 × 5 = 100 (Quarter of 400)
- 20 × 10 = 200 (Double century)
- 20 × 15 = 300 (Three hundred mark)
- 20 × 20 = 400 (Perfect square relationship)
- 20 × 25 = 500 (Half of thousand)
- 20 × 50 = 1000 (One thousand exactly)
7.3 Pattern Checklist
- All answers end in 0.
- All answers are even numbers.
- Each step increases by exactly 20.
- Table of 20 = Table of 10 doubled.
- Table of 20 = Table of 2 with zero added.
Mastering the table of 20 using the ×2 then add zero trick makes mental calculations fast and accurate. Regular practice with the complete table (1 to 20) and understanding the underlying patterns ensures you never make errors. This table is especially useful in percentage calculations, time problems, and money-related questions where multiples of 20 appear frequently. Keep practicing the trick until it becomes automatic and instant.
