Learn Hindi

How much of India speaks Hindi?  Is it the "common" language of India, in the way that Mandarin is for Chinese?

It's the national language of India,Indians know this language more or less, and can understand and communicate

Vic, Hindi is the National Language just as Susmita said.

Majority of the Indians use this language, English and Hindi are two common languages used here. Though there are other regional languages too but even the people who speak in a regional language know either one or both of the languages(Hindi and English).

OH ,THAT'S GREAT ,BUT HOW CAN I LEARN HINDI FROM YOU ,IS IF FREE ,DEAR TEACHER

see my students are trying to speak hindi

http://www.youtube.com/talkingbees.com

See

there is no perticular language for india
people speak many languages here
therefore  india is divided in 23 states based on languages spoken and each have its own language
as hindi is spoken by many people from different states it is selected as national language.
still most of people dont know hindi though its a national language of india.