shandilya is correct that you can directly to the math 3/8*5/9, however, depending on how you set it up (i.e. what type of primary your answer variable is set up as), you will end up either with a truncated integer (int) of zero, or a floating point number (i.e. a decimal number) of 0.06944444. (And no need to use BigInteger).
If you want your answer to be a fraction, you would need to create a Fraction class. Define it with two int's as instance variables to represent the numerator & denominator. Then create various methods for adding, subtracting, multiplying, etc. You would also probably want a reduce method, and perhaps a findCommonDenominator method. All the things you need to do true fraction math.
Then override Object's toString method to output the result as a fraction. [ January 15, 2005: Message edited by: Mark Vedder ]