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Squaring a Number ending in 5



m48ortalM48ortal on 02/04/2009

SquaringaNumberendingin5 Photo Ready to learn a "Mathmagic" shortcut? In another quiz, I showed how to multiply 2 two-digit numbers quickly. This shortcut is a special case of that multiplication. Think of any number that ends in 5. When you square your number, it will end in 25 (the last two places on the right - tens and ones). Your number lies halfway between two numbers that end in zero, or have a zero in the ones place. If we ignore the zeros and multiply the two numbers that are left, we get the rest of your answer. How fast you can do this depends only on how well you know your times tables. As an example, we will square 115. This number is halfway between 110 and 120, so 11 X 12 is 132 and since our answer has to end in 25, we get 13225. (I leave the commas out on purpose since in some parts of the world they are used like decimal points.) Remember - ignore the ones place, multiply the rest of your number times the next higher whole number, then put a 25 in the right two places. Ta-Da! With a little practice, you're a math whiz. So here's your practice. Good luck!
10 Questions




Rating:  (8.36/9)
Difficulty:  Challenging
Taken: 73 times

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Player: Level: % Correct: Time to Complete:
1
Challenged2 34100.00%    51.13 seconds    
2
Garrybl 284100.00%    55.49 seconds    
3
Idaman 79100.00%    56.41 seconds    
4
Fainodraino 113100.00%    71.37 seconds    
5
Pragadeesh 2100.00%    75.32 seconds    
6
Scrabq 76100.00%    80.01 seconds    
7
1mensaman 51100.00%    83.29 seconds    
8
Kateatebate 232100.00%    85.97 seconds    
9
Gilgamesh10 62100.00%    87.79 seconds    
10
Saiganesh 3100.00%    95.54 seconds    



Comments (6)
mcmahon
Mcmahon  (Level: 39.6)
Sat, 20th Feb '10 4:52 PM

a bit to hard!


fainodraino
Fainodraino  (Level: 113.1)
Fri, 5th Jun '09 10:08 AM

Thank you! That was really fun!


lcoverton
Lcoverton  (Level: 117.7)
Thu, 5th Feb '09 6:20 PM

So much fun. It took me a couple of questions to really get it. It was easy then.


leaston
Leaston  (Level: 42.6)
Thu, 5th Feb '09 10:55 AM

I like this.. need to get a little faster... i messed up on one of them and clicked next before I answered it lol!


scrabq
Scrabq  (Level: 76.7)
Wed, 4th Feb '09 7:58 PM

That was solid fun.








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