bx-zone.com says :-
More than 10000 schools around the world are affiliated to the IGCSE syllabus developed by Cambridge International Examination in 1988. Being a very popular English language curriculum, more than 400 schools across India offer the Cambridge curriculum which means that there are approximately 20000 students who are using the books provided by Cambridge IGCSE in one academic year. And with bx-zone becoming popular many of these 20,000 students visit bx-zone's online second hand bookstore either to buy used textbooks of Cambridge curriculum or list their Cambridge old books for sale like this one over here Extended mathematics for Cambridge igcse at 52% in the city of Pune