Back to Calculation Tips & Tricks
- even numbers 2 through selected 2-digit evens
- digits of square of repeating ones
- consecutive odds
- consecutive between 2 numbers
- sequence from 1 to selected 2-digit number
- sequence from 1 to selected 1-digit number and back
- sequences in the 10's
- sequences in the 20's
- sequences in the 30's
- sequences in the 40's
- sequences in the 50's
- sequences in the 60's
- sequences in the 70's
- sequences in the 80's
- series of doubles
- series of quadruples
- series of 10 numbers
- 1's repeating, divide by 9, subtract 21
- 8's repeating, divide by 9, subtract 10
- squares of two numbers
- reversing/adding/subtracting 3-digit numbers
- finding 2.5 percent
- finding 5 percent
- finding 15 percent
- finding 20 percent
- finding 25 percent
- finding 33 1/3 percent
- finding 40 percent
- finding 45 percent
- finding 55 percent
- finding 60 percent
- finding 70 percent
- finding 75 percent
a series of ten numbers
- Have a friend choose and write down a single-digit number. (Two digits for experts.)
- Ask your friend to name and note a third number by adding the first two.
- Name a fourth by adding the second and third. Continue in this way, announcing
each number, through ten numbers.
- Ask your friend to add up the ten numbers. You will give the answer before he
or she can finish:
The sum of all the terms of this series will be the seventh number multiplied
- If the numbers selected are 7 and 4:
- The series jotted down is: 4, 7, 11, 18, 29, 47, 76, 123, 199, 322.
- The seventh number is 76. 11 × 76 = 836
(use the shortcut for 11: 7 is the first digit, 6 is the third digit;
the middle digit will be 7 + 6, and carry the 1: 836).
- So the sum of the ten numbers is 836.
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30 September 1996
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