27/12/2024
Mathematics Tricks:
Multiply by 11 Easily
• Example: 52 \times 11
• Add the digits of the number: 5 + 2 = 7 .
• Place the result between the digits: 572 .
2. Square Numbers Ending in 5
• Example: 35^2
• Take the first digit (3) and multiply it by the next higher digit (4): 3 \times 4 = 12 .
• Append 25 to the result: 1225 .
3. Multiplying Large Numbers Near a Base
• Example: 98 \times 97 (near 100)
• Find the difference from 100: 98 = -2 , 97 = -3 .
• Subtract diagonally: 98 - 3 = 95 .
• Multiply the differences: -2 \times -3 = 6 .
• Combine results: 9506 .
4. Divisibility Rule for 3 and 9
• A number is divisible by 3 if the sum of its digits is divisible by 3.
• For 9, the sum of digits must be divisible by 9.
• Example: 123 : 1 + 2 + 3 = 6 (divisible by 3, but not by 9).
5. Quick Percentage Calculation
• Example: 25\% of 240
• Divide the number by 4 : 240 \div 4 = 60 .
6. Multiply Any Number by 5
• Example: 34 \times 5
• Divide the number by 2 : 34 \div 2 = 17 .
• Append 0 : 170 .
7. Finding the Square of a Number
• Example: 47^2
• Break it into (47)^2 = (50 - 3)^2 = 50^2 - 2(50)(3) + 3^2 .
• Compute: 2500 - 300 + 9 = 2209 .
8. Multiplying by 9 Trick
• Example: 9 \times 8
• Subtract 1 from 8 : 7 .
• The second digit is 9 - 7 = 2 .
• Result: 72 .
9. Add Fractions with Cross-Multiplication
• Example: \frac{3}{4} + \frac{5}{6}
• Cross multiply and add numerators: (3 \times 6) + (4 \times 5) = 18 + 20 = 38 .
• Multiply denominators: 4 \times 6 = 24 .
• Result: \frac{38}{24} .
10. Subtract from 1000 Easily
• Example: 1000 - 648
• Subtract each digit from 9 , except the last from 10 :
9 - 6 = 3 , 9 - 4 = 5 , 10 - 8 = 2 .
• Result: 352 .