Hi

Yes , you are eligible for doing B Pharma.

This is because,

To be eligible for B Pharma or bachelors in pharmacy, you must have passed your 12th board examination with physics chemistry and Biology/Mathematics and generally you need 50% marks  in aggregate to be eligible  . So both biology and mathematics students are eligible for B Pharma

So, it's not mandatory to have studied Biology to be eligible for B Pharma So being a maths student you ate definitely eligible for doing B Pharma

And ,

Your admission in B pharma is either on the basis of marks obtained by you in class 12th or through college or university level entrance examination

Thank you