Hello,
You are eligible to write Civil Services Exam if you have completed any degree. It is not necessary to have Mathematics in 11th standard if you are a Civil Services aspirant.
For more information regarding Civil Services Exam go through below link. The syllabus of Civil Services Exam is given in below link.
https://competition.careers360.com/articles/upsc-ias-syllabus/amp
All The Best!!
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