In what year did India adopt the decimal system for its currency?

The correct answer is 1957.

Historical Context of Indian Currency:
Prior to 1957, India followed a complex monetary system inherited from British rule. The Indian Rupee was subdivided into annas and pice:
• 1 Rupee = 16 Annas
• 1 Anna = 4 Pice (or 12 Pies)
• 1 Rupee = 64 Pice

Adoption of the Decimal System:
To streamline calculations and modernize the economy, the Indian Parliament passed the Indian Coinage (Amendment) Act in September 1955, authorizing the switch to a decimal currency system.

The decimal system officially came into effect on April 1, 1957. Under this new system:
• The Rupee was divided into 100 equal parts, initially called Naye Paise ("New Paise") to distinguish them from the old pre-decimal paise.
• In 1964, the prefix "Naye" was officially dropped, and the denomination simply became known as "Paise".