Easy Math Tricks to Speed Up Your Calculations

 Here are some fun and useful math tricks to impress your friends or speed up calculations:

1. Multiply Any Number by 5 Quickly

• Trick: For any number, divide it by 2. If the result is an integer, add 0 to the end. If it’s not, ignore the remainder and place 5 at the end.
• Example:
  $32\times 5$: Half of 32 is 16 → Answer: 160.
  $43\times 5$: Half of 43 is 21.5 → Ignore .5, and add 5 → Answer: 215.

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2. Check Divisibility by 3

• Trick: Add up all the digits of the number. If the sum is divisible by 3, so is the number.
• Example:
  $123$: $1+2+3=6$, which is divisible by 3 → Yes, $123$ is divisible by 3.

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3. Square a Two-Digit Number Ending in 5

• Trick: Multiply the first digit by the next higher number and add 25.
• Example:
  $25^2$: $2\times 3=6$, so $625$.
  $65^2$: $6\times 7=42$, so $4225$.

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4. Multiplication by 11

• Trick: For a two-digit number, add the digits together and place the result in the middle.
• Example:
  $23\times 11$: $2+3=5$, so $253$.
  $48\times 11$: $4+8=12$, so $4(12)8\to 528$.

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5. Subtract from 1000 Quickly

• Trick: Subtract each digit from 9, except the last one from 10.
• Example:
  $1000-357$: $9-3=6,9-5=4,10-7=3$, so $643$.

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6. Multiplying Two Numbers Close to 100

• Trick: Subtract each number from 100, subtract the results crosswise, and multiply the differences.
• Example:
  $98\times 96$:
  $(100-98)=2,(100-96)=4$, $98-4=94$, $2\times 4=8$, so $9408$.

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7. Find the Day of the Week for Any Date

• This one’s a bit longer but involves modular arithmetic and "key" days for months. Let me know if you’re curious to learn it! 😊