Hi Pravallika,
By the way,can you please mention to us which exam do you exactly want information about so that we may help you better.
Thank you.
There is no fixed percentage of importance of any single chapter in each subject. It's just that some chapters may be very important for examination point of view and some less important.You must follow your teachers' advice in this case as to which chapters or subjects hold high importance and which ones less.Also refer to your notes you've made,if any.
Also you can refer last year's question papers for the subjects you are looking for.You can get a rough idea as to how much time to devote to each chapter or subject.
All the best!
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