A member of Frederick II's court, John of Palermo, posed several questions based on Arab mathematical works for Fibonacci to solve.

In 1240, the Republic of Pisa honored Fibonacci (referred to as Leonardo Bigollo)[20] by granting him a salary in a decree that recognized him for the services that he had given to the city as an advisor on matters of accounting and instruction to citizens.

In the Liber Abaci (1202), Fibonacci introduced the so-called modus Indorum (method of the Indians), today known as the Hindu–Arabic numeral system,[25][26] with ten digits including a zero and positional notation.

The book showed the practical use and value of this by applying the numerals to commercial bookkeeping, converting weights and measures, calculation of interest, money-changing, and other applications.

The second section explains uses in business, for example converting different currencies, and calculating profit and interest, which were important to the growing banking industry.

[29][27][28] Liber Abaci posed and solved a problem involving the growth of a population of rabbits based on idealized assumptions.