SOLUTION
Express each fraction to their simplest form.
For 3/4, this is already in its simplest form since the denominator and numerator doesn't have a common factor.
For 6/8, we can further simplify it. The common factor between the denominator and numerator is 2. That is: \frac{6}{8}=\frac{3\times2}{4\times2}
With this, you can cancel 2 to simplify. We have: \frac{3\times2}{4\times2}=\frac{3}{4}
Hence, the simplified form of 6/8 is 3/4.
Since Jose and his sister bought 3/4 oil, which is the same amount, then none of them bought more than what the other did.
ANSWER: None, because they bought equal amounts.