Approximate CBSE to US grade conversion

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<li><p>The common app requests an approximate grade conversion to the US system. I studied in CBSE. What should my teachers enter there? </p></li>
<li><p>But my school grades in a queer way. They have “cut-off” marks in certain subjects like English, making it impossible to get a 100. In practice, our English papers are graded on something like 88.</p></li>
<li><p>Also, can I just send in my 10th, 12th board results + a sheet signed by my principal with 9th and 11th final exam results. My 9th and 11th report cards are hard to understand for anybody not in my school. So I just want to show them the final grade. It will be attested by the school with a school letter head. </p></li>
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<p>Thanks!</p>