Multiplying by 6
If you multiply 6 by an even number, the answer will end with the same digit. The number in the tens place will be half of the number in the ones place.
Example: 6 x 4 = 24
The Answer Is 2
- Think of a number.
- Multiply it by 3.
- Add 6.
- Divide this number by 3.
- Subtract the number from Step 1 from the answer in Step 4.
The answer is 2.
Same Three Digit Number
- Think of any three digit number in which each of the digits is the same. Examples include 333, 666, 777, 999.
- Add up the digits.
- Divide the three digit number by the answer in Step 2.
The answer is 37.
Six Digits Become Three
- Take any three digit number and write it twice to make a six digit number. Examples include 371371 or 552552.
- Divide the number by 7.
- Divide it by 11.
- Divide it by 13. (The order in which you do the division is unimportant.)
The answer is the three digit number
Examples: 371371 gives you 371 or 552552 gives you 552.
- A related trick is to take any three digit number.
- Multiply it by 7, 11, and 13.
The result will be a six digit number that repeats the three digit number.
Example: 456 becomes 456456.
The 11 Rule
This is a quick way to multiply two digit numbers by 11 in your head.
- Separate the two digits in your mind.
- Add the two digits together.
- Place the number from Step 2 between the two digits. If the number from Step 2 is greater than 9, put the ones digit in the space and carry the tens digit.
Examples: 72 x 11 = 792
57 x 11 = 5 _ 7, but 5 + 7 = 12, so put 2 in the space and add the 1 to the 5 to get 627
To remember the first seven digits of pi, count the number of letters in each word of the sentence:
“How I wish I could calculate pi.”
This gives 3.141592
Contains the Digits 1, 2, 4, 5, 7, 8
- Select a number from 1 to 6.
- Multiply the number by 9.
- Multiply it by 111.
- Multiply it by 1001.
- Divide the answer by 7.
The number will contain the digits 1, 2, 4, 5, 7, and 8.
Example: The number 6 yields the answer 714285.