Only one equation, two unknowns ??? But integer numbers !

- A bookseller sells pens 0,97 Euros and pencils 0,29 Euros.

At the end of the day he earned 40 Euros.

How many pens and pencils did he sell ?

Solution

Even better ! only one equation and 3 unknowns !

- The same bookseller, has set books of 15mm, 21mm and 35mm thickness in a
20cm high pile.

How many books of each ?

Solution

Methods and formulas.

Script to solve ax + by = c.