See if you want to give exam in English and Maths then u don't have to give practical exam and then u only have to appear in normal board exam if ur score is 75/80 then percentage will be calculated according to it 75/80*100=93.75 which is ur score out of 100. I m not sure but a tentative idea.Gud luck

I am also facing same problem about the 20 marks from school. The subjects are English and mathematics.If I am a private candidate then how will I give the internal assesments of English and mathematics.

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  The application forms for improvement exam will be available in the month of July or August.
  


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  Each form costs Rs. 10 and per subject the fees is Rs. 200
  


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  Forms can be collected from Syndicate Bank branches throughout Delhi and Regional Offices of CBSE for other regions.
  

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  Visit the official website,
  
  http://www.cbse.nic.in
  
  


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  Enter your CBSE board roll number in the first text box
  


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  Enter your 5 digit school number in the second text box and if you appeared as a private candidate and do not have a school, then enter 99999 in place of school number.
  


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  Enter your examination centre number by referring to your CBSE board admit card
  


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  Click on proceed and fill in your details
  


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  Make online payment or through E-Challan from the respective bank
  


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  Note down your application number and roll number that will be provided after payment is done
  


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  Follow the instructions on the confirmation page.