Hiya, tbh, I personally don't think it'd be necessary for you to do grade 10 again.. I'd think that they'd think highly of an IB qualification. Make sure to show them your result certificates and a letter from your secondary school to show that you studies there. Hmmm, Maths in India is really hard (even though there are many who are not good at it too) because when I came to the UK to do my A Level (maths), I found that I have covered most of the things in grade 10 India (which shouldn't have been the case cuz A level is a higher qualification). So you might want to look at CBSE grade 10 maths before starting because I assume IIT-JEE is rather mathsy and sciencey... I can't say much else because I came to UK from India and don't know how it'd work the other way round. Plus, I haven't done IB so don't know much about that either. But I've heard that IB is a really good qualification to have so don't fret too much. I think you'll be fine. Good luck...