Multipication Tricks
Multiplication Tricks
Multiplying by 11
Trick: Sum of digits goes in between.
Ex:
1. 11 × 23 → 2 + 3 = 5 → 253
2. 11 × 47 → 4 + 7 = 11 → carry → 517
3. 11 × 56 → 5 + 6 = 11 → carry → 616
4. 11 × 89 → 8 + 9 = 17 → carry → 979
5. 11 × 34 → 3 + 4 = 7 → 374
Multiplying by 12
Trick: Actually: Multiply by 12 = Multiply by 10 + Multiply by 2
Ex:
1. 12 × 25 → 250 + 50 = 300
2. 12 × 36 → 360 + 72 = 432
3. 12 × 44 → 440 + 88 = 528
4. 12 × 55 → 550 + 110 = 660
5. 12 × 66 → 660 + 132 = 792
Multiplying by 15
Trick: Half + original × 10
Ex:
1. 15 × 20 → 20 + 10 = 30 → 300
2. 15 × 40 → 40 + 20 = 60 → 600
3. 15 × 60 → 60 + 30 = 90 → 900
4. 15 × 75 → 75 + 37.5 = 112.5 → 1125
5. 15 × 88 → 88 + 44 = 132 → 1320
Multiplying by 25
Trick: Divide number by 4 × 100
Ex:
1. 25 × 12 → 12/4 = 3 → 300
2. 25 × 16 → 16/4 = 4 → 400
3. 25 × 20 → 20/4 = 5 → 500
4. 25 × 24 → 24/4 = 6 → 600
5. 25 × 28 → 28/4 = 7 → 700
Multiplying by 50
Trick: Divide number by 2 × 100
Ex:
1. 50 × 14 → 14/2 = 7 → 700
2. 50 × 26 → 26/2 = 13 → 1300
3. 50 × 38 → 38/2 = 19 → 1900
4. 50 × 42 → 42/2 = 21 → 2100
5. 50 × 68 → 68/2 = 34 → 3400
Multiplying by 125
Trick: Divide number by 8 × 1000
Ex:
1. 125 × 16 → 16/8 = 2 → 2000
2. 125 × 24 → 24/8 = 3 → 3000
3. 125 × 32 → 32/8 = 4 → 4000
4. 125 × 40 → 40/8 = 5 → 5000
5. 125 × 56 → 56/8 = 7 → 7000
Multiplying by 5
Trick: Multiply by 10 and divide by 2
Ex:
1. 5 × 12 → 120/2 = 60
2. 5 × 24 → 240/2 = 120
3. 5 × 36 → 360/2 = 180
4. 5 × 48 → 480/2 = 240
5. 5 × 60 → 600/2 = 300
Multiplying by 105
Trick: Multiply by 100 + original number
Ex:
1. 105 × 20 → 2000 + 20 = 2020
2. 105 × 35 → 3500 + 35 = 3535
3. 105 × 50 → 5000 + 50 = 5050
4. 105 × 60 → 6000 + 60 = 6060
5. 105 × 80 → 8000 + 80 = 8080
Multiplying by 125
Ex:
1. 125 × 32 → 32/8 = 4 → 4000
2. 125 × 40 → 40/8 = 5 → 5000
3. 125 × 48 → 48/8 = 6 → 6000
4. 125 × 56 → 56/8 = 7 → 7000
5. 25 × 64 → 64/8 = 8 → 8000
Multiplying by 101
Trick: Put number + number → for 3-digit, split
Ex:
1. 101 × 23 → 23 + 23 = 2323
2. 101 × 45 → 45 + 45 = 4545
3. 101 × 12 → 12 + 12 = 1212
4. 101 × 56 → 56 + 56 = 5656
5. 101 × 89 → 89 + 89 = 8989
Multiplying by 99
Trick: Always “Multiply by 100 → Subtract original number”
Ex:
1. 99 × 42 → 4200 − 42 = 4158
2. 99 × 56 → 5600 − 56 = 5544
3. 99 × 23 → 2300 − 23 = 2277
4. 99 × 87 → 8700 − 87 = 8613
5. 99 × 65 → 6500 − 65 = 6435
Multiplying by 1001
Trick: Multiply by 1000 + Number → Just write the number twice
Ex:
1. 1001 × 23 → 23,000 + 23 = 23,023 → or just write 23 twice: 23023
2. 1001 × 45 → 45,000 + 45 = 45,045 → write 45 twice
3. 1001 × 12 → 12,000 + 12 = 12,012 → write 12 twice
4. 1001 × 56 → 56,000 + 56 = 56,056 → write 56 twice
5. 1001 × 89 → 89,000 + 89 = 89,089 → write 89 twice