make24

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The aim of the game is to manage four digit numbers by elementary arithmetic operations, to generate the result of 24.
The numbers are generated randomly.Each of the random numbers must be used 1x and only 1x.
Allowed are only elementary arithmetic operations (+, -, *, /) and the use of parentheses.
Not allowed are other computational operations such powers, roots, faculties etc.
Also not allowed to combine two or three digits to a multi-digit number.
Type errors can be corrected with "undo".
One possible solution is displayed under "help".
Examples:
given: 6, 8, 9, 9 solution: 8 × ( 9 + 9 ) / 6 = 24
given: 1, 3, 4, 8 solution: 4 × ( 8 - 3 + 1 ) = 24 not allowed: 38 - 14 = 24
given: 1, 3, 4, 6 solution: 6 / ( 1 - 3 / 4 ) = 24