Recreational math

• Recreational math
  Posted by Clay Death on 02 May, 2015 22:58
• Doodling in Math and more
  
  https://www.khanacademy.org/math/recreational-math/vi-hart
  
  
  
  
  Puzzles
  
  https://www.khanacademy.org/math/recreational-math/puzzles
  
  
  
  
  Math warmups
  
  https://www.khanacademy.org/math/recreational-math/math-warmup
  
  
  
  
  
• 
  
• #1 Reply
  Posted by JFoshia on 27 Aug, 2015 10:51
• A quick little math trick: A Fibonacci Sequence problem.
  
  Can you add these numbers up in your head?
  
  2
  2
  4                            Here is the trick: Take the 7th number down (26)
  6                            Add the tens digit to the number: 26+2=28
  10                          Then you just tack on the ones digit at the end! 286
  16                          So, all ten numbers in this sequence to the left will add up to 286
  26
  42
  68
  110
• 
  
• #2 Reply
  Posted by JFoshia on 27 Aug, 2015 10:56
• Squaring 2-Digit Numbers That End In 5
  
  Example:
    35
  x35
  
  
  The answer will end in 25 (because 5x5=25) so write that down.
  Then, look at the tens digit (3). Multiply that number by the number that is one greater than it: 4
  Write that answer in front of the 25.
  So your answer will be 1,225
  
  It works for squaring any 2-digit number that ends in 5.
  
             
•