Mental Mathematics: Multiplications

Here are some quick and effective multiplication techniques to speed up mental math calculations.

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1️⃣ Multiplying by 5 Trick

✅ Method:

• If the number is even → Divide by 2, then add 0.
• If the number is odd → Subtract 1, divide by 2, then add 5.

✅ Example:
🔹 48 × 5 → (48 ÷ 2) = 24 → Add 0 → 240
🔹 37 × 5 → (36 ÷ 2) = 18 → Add 5 → 185

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2️⃣ Multiplying by 9 Trick (Finger Method)

✅ Method:

• Spread both hands.
• For 9 × N, fold down the Nth finger.
• Left-hand fingers = Tens place, Right-hand fingers = Ones place.

✅ Example:
🔹 9 × 7 → Fold the 7th finger → 6 fingers left, 3 fingers right → Answer: 63

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3️⃣ Multiplying by 11 Trick

✅ Method:

• For 2-digit numbers (AB): Add digits together and place in the middle.

✅ Example:
🔹 34 × 11 → 3 (3+4) 4 → Answer: 374
🔹 52 × 11 → 5 (5+2) 2 → Answer: 572

(If sum is ≥10, carry over the extra digit.)
🔹 89 × 11 → 8 (8+9=17) 9 → Carry over → 979

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4️⃣ The "Half & Double" Trick (For Even & Odd Multiplications)

✅ Method:

• If one number is even, halve it and double the other.

✅ Example:
🔹 16 × 25 → (8 × 50) = 400
🔹 48 × 75 → (24 × 150) = (12 × 300) = 3600

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5️⃣ Multiplying Numbers Close to 100

✅ Method:

1. Find how much each number is below 100.
2. Subtract crosswise.
3. Multiply the differences.

✅ Example:
🔹 97 × 96

• 97 is 3 below 100, and 96 is 4 below 100.
• Cross subtract: 97 - 4 = 93
• Multiply remainders: 3 × 4 = 12
• Final Answer: 9312

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6️⃣ Vedic Multiplication (Cross Multiplication Method)

✅ Method:

1. Multiply unit digits.
2. Cross-multiply and sum.
3. Multiply tens digits.

✅ Example:
🔹 32 × 21

• 2 × 1 = 2
• (3×1) + (2×2) = 3 + 4 = 7
• 3 × 2 = 6
• Final Answer: 672

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🎯 Bonus: Squaring Numbers Ending in 5

✅ Method:

1. Multiply the tens digit by itself +1.
2. Place 25 at the end.

✅ Example:
🔹 35² → (3 × (3+1)) = 12, then add 25 → 1225
🔹 85² → (8 × 9) = 72, then add 25 → 7225

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📌 Summary of Speed Math Tricks

Trick	Example	Answer
Multiplying by 5	38 × 5	190
Multiplying by 9 (Finger Method)	9 × 6	54
Multiplying by 11	45 × 11	495
Half & Double	16 × 25 → 8 × 50	400
Multiplying Near 100	97 × 96	9312
Vedic Multiplication	32 × 21	672
Squaring Numbers Ending in 5	75²	5625

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