If you have two marksheets, one from ISC and one from NIOS On-Demand in Mathematics, and you're wondering about your eligibility for admission to Delhi University (DU), here are the key points to consider:

1. Eligibility Criteria : Delhi University generally accepts marks from recognized boards like ISC and NIOS. You should check the specific eligibility criteria for the course you are applying to, especially regarding the acceptance of subjects from different boards.

2. Combination of Marksheets : If you have marks in different subjects from different boards, DU typically allows combining them, provided both marksheets are from recognized boards and you meet the minimum eligibility criteria for the course.

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3. Documentation : Ensure that you have all the necessary documents, including both marksheets, passing certificates, and any other required documentation. DU might ask for an equivalency certificate or an explanation of the combination of marksheets.

4. Subject Requirements : Verify that you meet the subject-specific requirements for the course, especially in mathematics if it is a core requirement for the course you're applying to.

5. Consult DU Admissions : To be sure, it's advisable to contact the DU admissions office directly or visit their official website for detailed guidance. They can provide specific instructions on how to proceed with marksheets from different boards.

6. Previous Year Trends : Check previous years' admission guidelines or ask current students if they have had similar cases. This might give you an idea of how DU handles such situations.

As long as both marksheets are from recognized boards and you meet the subject and percentage criteria, you should be eligible to apply to DU. However, confirming with DU directly is always a good step to avoid any issues during the admission process.