Read Text File And Perform Operation On Specific Columns

I am somewhat of a java newbie (learned it awhile back and just getting back to programming some again.) I have a text file of data much larger than this, but here are the first ten rows and first 10 columns.

39755320111041730140.633038085-2.117082366149.069997
39850320111041730150.633038085-2.117082511148.309997
39955320111041730160.633037998-2.117082293149.509997
40055320111041730170.633037945-2.117082351149.239997
.......

I can read and write all the data back out to files. But I am not sure about a few things.

First would it be best to use BufferedReader and OutputStream such as:

public static void main(String[] args) throws IOException {
BufferedReader bReader = new BufferedReader(new FileReader ("testdata.txt"));
BufferedOutputStream bytesOut = new BufferedOutputStream(new FileOutputStream ("outfile.txt"));

Second, I was then going to initialize an array but I might have 30 or more columns of data, of which I might perform and output only 10 columns to my output.txt file so is this a good way?

Third, I only want to perform operations (such as average the data, convert units or multiply two columns together) on 10 of the 30 plus columns and print out results to output.txt file. For example, In testdata.txt file above, I want to skip first seven columns. I then want to take column 8 and multiply by 100 then divide by 3 and output result to output file. I want to do same for column 9. Column 10 I want to multiply by different number (by 3.5).