Yes! You can list it as an extra curricular activity. They look for students that are active in their schools and specially one with good grades in math, science, and English, these are the most important subjects for these schools and an event that improves one of these like Math Olympics does definitely give you a little edge over the average applicant.
Disha publication books for olympiad exams might help you if you are looking for class 8th olympiad books.
he
You can download papers with answers on google just type in Jumior Maths Olympiad Papers
yes
You can prepare for Maths and Science Olympiad by logging / taking subscription in the Reflective Learn website. They provide sample and model test paper and prepare you to competitive exams like NSO, IMO and other Olympiad exams.
the hardest maths sum is the question 6 of the 1988 maths olympiad
You can use website http://www.examhelp.in for preparing for Maths Olympiad for class 4,5 and 6.
no fifth std
1st february 2011
by answering all questions correctly!
Just go on site sofworld.org
Follow the attached related link for general information on the Math Olympiad program, including sample problems.