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 **Includes - Guess24.** activity
 
 [[_TOC_]]
 
 # Development notes
 
 ## Data
 
 The [4 numbers](https://www.4nums.com/game/) site provides data on all possible solutions.
 I used this [table](https://www.4nums.com/solutions/allsolutions/) to get problems with valid solutions.
 And this other [table](https://www.4nums.com/game/difficulties/) which gives statistics on the success rate and average solution time.
 These data come from a population of Internet users who are probably adults.
 
 These data are in the files `tools/Guess24-solutions.csv` and `tools/Guess24-difficulty.csv`. They are not used in the activity but are used to generate
 `guess24.json`.
 
 ## Data problem
 
 Some solutions require an intermediate result in the form of a fraction (read this [page](https://www.4nums.com/solutions/fractions/)).
 Example: **2 3 5 12** has the unique solution **12/(3-5/2)**, which is not at the level of a primary school pupil.
 
 ## Preparing the data
 
 The data milling script is written in `php`. This language can be used with the command line and is available in all Linux distributions.
 It prepares the data but is not useful for running the activity.
 
 ### build-datas.php
 
 * Use it in the `guess24/tools/` directory: `$ php build-datas.php`.
 * It reads the two `.csv` files to extract useful data.
 * And selects problems according to these rules:
 
     * Eliminates solutions with a fractional intermediate result.
     * Eliminates solutions with an average resolution rate below a certain threshold (variable `$limitRate`).
     * Classifies problems into three complexity categories:
     
         **1**: problems with at least one solution containing only addition and/or subtraction.
         **2**: problems with at least one solution containing one multiplication.
         **3**: problems with division required.
 
 This script produces the file `resource/guess24.json` and outputs a report to the terminal :
 
     Problems with a solved rate greater than 80%
     --------------------
     Complexity 1: 217 problems
     Complexity 2: 742 problems
     Complexity 3: 118 problems
     Total: 1077 problems
     --------------------
     Output file: ../resource/guess24.json
     Output file size: 173673 bytes
     103 solutions rejected for a rational intermediate result
 
 `php build-datas.php --help` gives the possibles options:
 
     Usage: php build-datas.php [OPTIONS]
     Create file `guess24/resource/guess24.json` from `Guess24-difficulty.csv` and `Guess24-solutions.csv`.
     Print a report on stdout.
     
     Options
       -v, --verbose              print informations on rejected formulas.
       -s, --solutions            no solutions in output file.
       -r, --rate [LIMITRATE]     set minimum solved rate required (default 80).
       -h, --help                 display this help and exit.
 
 Extract from `resource/guess24.json` :
 
     [
         {
             "puzzle": "1 1 12 12",
             "solutions": [
                 "12+12+1-1"
             ],
             "complexity": 1
         },
         {
             "puzzle": "1 1 2 6",
             "solutions": [
                 "(1+1)*6*2",
                 "(2+1+1)*6"
             ],
             "complexity": 2
         },
         {
             "puzzle": "1 1 2 11",
             "solutions": [
                 "11*2+1+1",
                 "(1+1)*11+2",
                 "(11+1)*2*1"
             ],
             "complexity": 2
         }
     ]
 
 The data weight 170Kb.
 Removing the solutions brings it down to 70Kb.
 
 To get the smallest file: `$ php build-datas.php -s -c`
 
 ## Levels of difficulty.
 
 The `Data.qml` files contain three pieces of data:
 
     data: [
         {
             "count": 20,
             "complexities": [ 2, 3 ],
             "operatorsCount": 4
         }
     ]
 
 `complexities` is the list of desired `complexities` in the level (from 1 to 3).
 `operatorsCount` controls the number of operators displayed (in order `+`, `-`, `×`, `÷`).
 
 The difficulty levels use complexities as follows:
 
   **1** Uses complexity 1 problems (217 problems)
   **2** Uses problems of complexity 1 and 2 (217 + 742 problems)
   **3** Uses complexity 2 problems (742 problems)
   **4** Uses complexity 2 and 3 problems (742 + 118 problems)
   **5** Uses complexity 3 problems (118 problems)
 
 In the example above, the activity will randomly select a list of 20 problems from the 860 possibles (742 + 118).
 
 ## Interface
 
 I was inspired by this site: [Y8](https://fr.y8.com/games/make_24).
 
 Negative or fractional intermediate results are rejected by a small animation.
 
 Keyboard interface:
 
   * Arrows to move from one value to another.
   * Space, Return or Enter to select the next value.
   * The +, -, * and / keys for arithmetic operations.