Multiplying and dividing fractions are essentially the same process which you multiply the numbers straight across and no need for common denominators. Except in division of fractions, the second fraction is flipped so that the denominator is on the top and the numerator is on the bottom (reciprocal).
First we'll figure out how much he spent. $25 times 8 (weeks)= $200. Then we subtract that $200 from the total $500. $500-$200=$300. A. Trent has $300 left in his saving