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Mathematical tricks Lorena

Made by Lorena for eTwinning project "A world of interesting and fun mathematics, we are happy!"

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MATHEMATICAL
TRICKS
Lorena Pende
1. DIVISIBILITI TRICKS
You can easily figure out if numbers are divisible using these tricks
for all numbers without fractions and decimals.
Numbers are…
• Divisible by 2 if the number's last digit is divisible by 2 (e.g. 298).
• Divisible by 3 if the sum of the digits of the number are divisible by 3
(501 is because 5 + 0 + 1 equals 6, which is divisible by 3).
• Divisible by 4 if the last two digits of the number are divisible by 4
(2,340).
• Divisible by 5 if the last digit is 0 or 5 (1,505)
• Divisible by 6 if the rules of divisibility for 2 and 3 work for that number
(408).
• Divisible by 9 if the sum of digits of the number are divisible by 9 (6,390
because 6 + 3 + 9 + 0 equals 18, which is divisible by 9).
• Divisible by 12 if the rules of divisibility for 3 and 4 work for that number
(408).
2. FINGER MATH FOR
MULTIPLICATION TABLE OF 9
If you have problems remembering the multiplication table of 9, try
this finger math trick
• Open both of your hands, extending your fingers, in front of you.
• To multiply 9 by 5, fold down your fifth finger from the left. To multiply 9 by
6, fold down your sixth finger from the left, and on.
• Get the answer to 9 by 5 by counting your fingers on either side of the
bent finger and combining them: 4 and 5 makes 45 (9 x 5) and 5 and 4
makes 54 (6 x 9).
• Now you can quickly figure out the multiplication table of 9 all the way up
to 9 times 10.
3. THE RULE OF 72
If you have to estimate the effects of compound interest use the rule of 72
and skip the financial calculator
Divide the number 72 by your target interest rate, and you get the
approximate number of years that it will take for your money to double.
If you were to invest in a 0.9% CD, it would take about 80 years for your
money to double. (72 divided by 0.9)
4. 3 DIGIT NUMBER TRICK
This is a fun trick you can use to
impress your friends
• Think of a 3 digit number.
• Multiply it with x7
• Multiply it with x11
• Multiply it with x13
• You will get a 6 digit number that is
combined of 2, 3 digit numbers the
person thought od in the beggining
(Number: 456, Answer: 456456)
Using this trick you can easily square two digit numbers that
end with 5.
• Multiply the first digit by itself, plus 1 (35 → 3 x (3+1) =12)
• Put a 25 at the end (352 =1225)
5. EASY SQUARE A 2 DIGIT NUMBER
THAT ENDS IN 5

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Mathematical tricks Lorena

  • 2. 1. DIVISIBILITI TRICKS You can easily figure out if numbers are divisible using these tricks for all numbers without fractions and decimals. Numbers are… • Divisible by 2 if the number's last digit is divisible by 2 (e.g. 298). • Divisible by 3 if the sum of the digits of the number are divisible by 3 (501 is because 5 + 0 + 1 equals 6, which is divisible by 3). • Divisible by 4 if the last two digits of the number are divisible by 4 (2,340). • Divisible by 5 if the last digit is 0 or 5 (1,505) • Divisible by 6 if the rules of divisibility for 2 and 3 work for that number (408). • Divisible by 9 if the sum of digits of the number are divisible by 9 (6,390 because 6 + 3 + 9 + 0 equals 18, which is divisible by 9). • Divisible by 12 if the rules of divisibility for 3 and 4 work for that number (408).
  • 3. 2. FINGER MATH FOR MULTIPLICATION TABLE OF 9 If you have problems remembering the multiplication table of 9, try this finger math trick • Open both of your hands, extending your fingers, in front of you. • To multiply 9 by 5, fold down your fifth finger from the left. To multiply 9 by 6, fold down your sixth finger from the left, and on. • Get the answer to 9 by 5 by counting your fingers on either side of the bent finger and combining them: 4 and 5 makes 45 (9 x 5) and 5 and 4 makes 54 (6 x 9). • Now you can quickly figure out the multiplication table of 9 all the way up to 9 times 10.
  • 4. 3. THE RULE OF 72 If you have to estimate the effects of compound interest use the rule of 72 and skip the financial calculator Divide the number 72 by your target interest rate, and you get the approximate number of years that it will take for your money to double. If you were to invest in a 0.9% CD, it would take about 80 years for your money to double. (72 divided by 0.9)
  • 5. 4. 3 DIGIT NUMBER TRICK This is a fun trick you can use to impress your friends • Think of a 3 digit number. • Multiply it with x7 • Multiply it with x11 • Multiply it with x13 • You will get a 6 digit number that is combined of 2, 3 digit numbers the person thought od in the beggining (Number: 456, Answer: 456456)
  • 6. Using this trick you can easily square two digit numbers that end with 5. • Multiply the first digit by itself, plus 1 (35 → 3 x (3+1) =12) • Put a 25 at the end (352 =1225) 5. EASY SQUARE A 2 DIGIT NUMBER THAT ENDS IN 5
  • 7. CREDITS: This presentation template was created by Slidesgo, including icons by Flaticon, and infographics & images by Freepik Thanks! Do you have any questions?