Place + and  signs between digits to make 100.
123456789
Mr. Bowen's Fifth Grade 

Can you solve this puzzle?
Place + and  signs between digits to make 100. 123456789
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Have you ever noticed the string of digits right above the bar code on the back of a book? It is called an ISBN  International Standard Book Number  and every published book has a unique one. You can think of it as a book's ID number. The last digit in a 10digit ISBN (for books published prior to 2007) is called a check digit. A check digit is calculated from the previous 9 digits and is used to ensure the entire number is valid (that is, to ensure that someone didn't just make a typo when copying it down). Interestingly, some books have a letter X at the end of the number. That's because the check digit is calculated in Base11! The Roman numeral X is used in place of 10 as a digit. Read more about how check digits are made here:
https://en.wikipedia.org/wiki/International_Standard_Book_Number#ISBN10_check_digit_calculation Here is a calculator for ISBN check digits: https://planetcalc.com/7744/ UPC Codes (the digits at the bottom of a bar code) also have a check digit. Here is how they are formed: https://en.wikipedia.org/wiki/Check_digit#UPC Does pi = 4? Watch this video:
http://www.viewpure.com/kTVRopTVjpQ?start=0&end=0 But wait... since a computer screen is comprised of square pixels, does pi equal 4 for any circle drawn on a computer? Check out this online version of the Kakooma Puzzle by Greg Tang. I recommend starting with the practice version (and of course read the directions). These supposedly take an average adult around 4 minutes to solve.
Can you solve this challenge that is based on the Proof card game?
https://www.proofmathgame.com/mathpuzzles/76 Here is their archive of past challenges: https://www.proofmathgame.com/mathpuzzles/past Nine cards, each uniquely marked with a singledigit from 1 to 9, are randomly dealt to three players, each player receiving three cards. Every player sees his own cards, but is unaware of the cards in other players' hands.
Each player declares the sum of the three cards in his own hands. Based upon this information, the players try to guess the cards in their opponents' hands. Imagine players A, B, and C play this game, and the following conversation ensues: A: The sum of my cards is 14. B: The sum of my cards is 15. C. The sum of my cards, obviously, is 16. A. I can't guess any card in B's hand. B. I can't guess any card in C's hand. C. I know the cards in everyone's hands. What are the cards in player B's hand? Explain your reasoning. If the white triangle is worth 1, what is the value of each other polygon? Source (and many more of these puzzles): https://photos.google.com/share/AF1QipPUhHweMG3cpSQ2CRL0scB2KtIKi2D6UFLrLtVuBNpr_zUWsqce6nzZGmkWi5UWA?key=QlZfb2Rtd05vbXRiVklUSldiUGVTSVMxd2hINXJn
How many numbers can you classify in 60 seconds? My best is 47.
http://isthisprime.com/game/ Some interesting stats on the game: http://isthisprime.com/game/record.php 
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