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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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Quiz Leaderboard
Player: Level: % Correct: Time to Complete:
Challenged2 34100.00%    51.13 seconds    
Garrybl 284100.00%    55.49 seconds    
Idaman 79100.00%    56.41 seconds    
Fainodraino 113100.00%    71.37 seconds    
Pragadeesh 2100.00%    75.32 seconds    
Scrabq 76100.00%    80.01 seconds    
1mensaman 51100.00%    83.29 seconds    
Kateatebate 232100.00%    85.97 seconds    
Gilgamesh10 62100.00%    87.79 seconds    
Saiganesh 3100.00%    95.54 seconds    

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

a bit to hard!

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

Thank you! That was really fun!

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

That was solid fun.

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