Squaring a Number ending in 5
M48ortal on 02/04/2009
Ready to learn a "Mathmagic" shortcut? In another quiz, I showed how to multiply 2 twodigit 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. TaDa! With a little practice, you're a math whiz. So here's your practice. Good luck!

Quiz Leaderboard
Player:  Level:  % Correct:  Time to Complete:  
1  Challenged2  34  100.00%  51.13 seconds 
2  Garrybl  276  100.00%  55.49 seconds 
3  Idaman  79  100.00%  56.41 seconds 
4  Fainodraino  111  100.00%  71.37 seconds 
5  Pragadeesh  2  100.00%  75.32 seconds 
6  Scrabq  76  100.00%  80.01 seconds 
7  1mensaman  51  100.00%  83.29 seconds 
8  Kateatebate  227  100.00%  85.97 seconds 
9  Gilgamesh10  62  100.00%  87.79 seconds 
10  Saiganesh  3  100.00%  95.54 seconds 
Comments (6)
Mcmahon (Level: 39.6)
Sat, 20th Feb '10 4:52 PM
a bit to hard!
Thank you! That was really fun!
So much fun. It took me a couple of questions to really get it. It was easy then.
I like this.. need to get a little faster... i messed up on one of them and clicked next before I answered it lol!
That was solid fun.