Math Tricks
PHONE NUMBER TRICK
1. Get a calculator. (You won't be able to do this one in your head).
2. Key in the first three digits of your phone number (NOT the area code).
3. Multiply by 80.
4. Add 1.
5. Multiply by 250.
6. Add the last 4 digits of your phone number.
7. Add the last 4 digits of your phone number again.
8. Subtract 250.
9. Divide by 2.
Do you recognize the answer???
1. Get a calculator. (You won't be able to do this one in your head).
2. Key in the first three digits of your phone number (NOT the area code).
3. Multiply by 80.
4. Add 1.
5. Multiply by 250.
6. Add the last 4 digits of your phone number.
7. Add the last 4 digits of your phone number again.
8. Subtract 250.
9. Divide by 2.
Do you recognize the answer???
GUESS A BIRTHDAY
by Irving Adler in Magic House of Numbers
Give the following instructions to a friend:
1. Think of two numbers: (1) the number of the month in which you were born, and (2) the number of the day of the month on which you were born.
2. Multiply the month number by 5.
3. Add 6.
4. Multiply by 4.
5. Add 9.
6. Multiply by 5.
7. Add the Day on which you were born.
8. Subtract 165 to reveal the month and day that your friend was born. The last two digits give the day, and the other digits give the month.
Why does this work? Why don't you use algebra to prove it? Then following the instructions above: (1) Let m = month and d = day. (2) Multiply the month number by 5, so 5m. (3) Add 6, so 5m + 6. (4) Multiply by 4, so 20m + 24. (5) Add 9, so 20m + 33. (6) Multiply by 5, so 100m + 165. (7) Add the day on which you were born, so 100m + d + 165. (8) Subtract 165, so 100m + d. The 100 just moves the month over 2 places!
IS THAT YOUR FINAL ANSWER?
1. Have someone pick a number between 1 and 9.
2. Using a calculator, multiply your number by 9.
3. Multiply it by 12,345,679 (notice there is no 8 in that number).
4. Have the person show you the result so you can tell him the original number he selected! How? Easy. If he selected 5, the final answer is 555,555,555. If he selected 3, the final answer is 333,333,333. The reason: 9 x 12345679 = 111111111. You multiplied your digit by 111111111. (By the way, that 8-digit number (12,345,679) is easily memorized: only the 8 is missing from the sequence).
by Irving Adler in Magic House of Numbers
Give the following instructions to a friend:
1. Think of two numbers: (1) the number of the month in which you were born, and (2) the number of the day of the month on which you were born.
2. Multiply the month number by 5.
3. Add 6.
4. Multiply by 4.
5. Add 9.
6. Multiply by 5.
7. Add the Day on which you were born.
8. Subtract 165 to reveal the month and day that your friend was born. The last two digits give the day, and the other digits give the month.
Why does this work? Why don't you use algebra to prove it? Then following the instructions above: (1) Let m = month and d = day. (2) Multiply the month number by 5, so 5m. (3) Add 6, so 5m + 6. (4) Multiply by 4, so 20m + 24. (5) Add 9, so 20m + 33. (6) Multiply by 5, so 100m + 165. (7) Add the day on which you were born, so 100m + d + 165. (8) Subtract 165, so 100m + d. The 100 just moves the month over 2 places!
IS THAT YOUR FINAL ANSWER?
1. Have someone pick a number between 1 and 9.
2. Using a calculator, multiply your number by 9.
3. Multiply it by 12,345,679 (notice there is no 8 in that number).
4. Have the person show you the result so you can tell him the original number he selected! How? Easy. If he selected 5, the final answer is 555,555,555. If he selected 3, the final answer is 333,333,333. The reason: 9 x 12345679 = 111111111. You multiplied your digit by 111111111. (By the way, that 8-digit number (12,345,679) is easily memorized: only the 8 is missing from the sequence).