I invested in a 100 percentage medical mutual fund. I bought the funds with about 3200. After some months I realized that about 50 of the money was from usury. Should I deduct just the interest the 50 could have made or should I do away with the whole interest I have made?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

If you mean the sum of 50 Dollars of your capital (3200) was from Riba, then you have to get rid of such an amount, i.e. to spend the 50 Dollars and its interest.

But, if you mean the capital invested in shares that entitles you to receive 50 Dollars as Riba, then you have to get rid of this sum only.

Allah Says (interpretation of meaning): {O you who have believed, fear Allah and give up what remains [due to you] of interest, if you should be believers. And if you do not, then be informed of a war [against you] from Allah and His Messenger. But if you repent, you may have your principal - [thus] you do no wrong, nor are you wronged).} [Quran 2:278-279]

Know that investment with a Riba-taking financial institution is strictly prohibited.

Allah knows best.