Some interesting math puzzles
From the collection of P. Narayanan (Amazing Vijay’s father)
The 9 principle:
Puzzle: Write down any 3 digit number. Reverse it. Subtract the smaller number from the larger number. Now if you tell me the first or the last digit, I can tell you the other two digits of the answer.
Answer: The answer will always be x9y and first and last digit will add up to 9 also. So tell them that the middle digit is 9 and then subtract from 9 to come up with the other digit
Puzzle: Write down any 3 digit number. Reverse it. Subtract the smaller number from the larger number. Now reverse the answer and add the 2 numbers together. I can tell you the answer.
Answer: It is always 1089
Quick calculations:
Finding the square
of any number ending with 5.
First digit x (first digit+1) and
then last 2 digits are always 25
E.g 35 x 35 = 3x4 = 12, so the
answer is 1225
E,g 85 x 85 = 8x9 = 72, so answer is 7225
Finding the square of any numbers starting with 5
First 2 digits are (25+second digit) ; Last 2 digits are the square of the second digit
E.g. 56 x 56 = 25+6 = 31, so the answer is 3136
E.g. 52 x 52 = 25+2 = 27, so the answer is 2704
Multiplying by 11.
Write down the last digit, Add 2 digits and write down answer to the left. Write first digit to left of this.
E.g. 23 x 11 = 2 (2+3)=5) 3 ->253
Sometimes
you have to carry over – but then this may not be so quick
E.g. 98 x 11 = (9+1 (carry)) (9+8)=7 and carry 1 8 -> 1078
What is GTTTT ? If you know Tamil, the answer is “Oru G nalu T” or “Originality”
Did you know that the letters A, B, C or D do not appear in the spelling of any number from 1 to 99.
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