Number puzzles as math training and mental jogging
The puzzle system used at MathematicalPuzzles.com is available in two versions which can either be solved online or in part downloaded as a PDF file. Altogether 378,028 math puzzles are available free of charge.
The simplified version is aimed mainly at pupils from Class 2 of the primary/ elementary school (7 years +), who can use it to practice the four basic arithmetical skills. The feeling of success will generate enthusiasm for math. In the math problems five numbers between 1 and 9 are combined using multiplication, division, addition and subtraction. How many numbers are provided in advance as 'clues' depends on the level of difficulty selected. Select math problems with 5 numbers and solve them online.
Because of its demands in terms of mental arithmetic, concentration, logic and memory the full version of the number puzzles appeals in particular to young people and adults who wish to increase and retain their mental fitness and enjoy solving problems. Nine numbers are combined by means of the four basic arithmetical skills  and the rule about multiplication/division ahead of addition/subtraction doesn't apply! Select math problems with 9 numbers and solve them online.
Rules: 
You enter a number from 1 to 9 in the squares in such a way that they match the solution. Numbers can only be used once.
(In the full version the rule about multiplication/division ahead of addition/subtraction doesn't apply)

There are 50,456 math problems for children and 327,572 brain teasers for young people from 10 years upwards – divided into a range of different patterns and levels of difficulty. All the problems have only a single solution and are limited to whole numbers without decimal points.
