Five students have the marks 92, 78, 85, 64, 78.

Mean: the total is $397$, and $397 \div 5 = 79.4$.

Median: sorted: $64, 78, 78, 85, 92$. The middle value is $78$.

Standard deviation: the distances from the mean are $12.6, -1.4, 5.6, -15.4, -1.4$. The squares are about $158.8, 2.0, 31.4, 237.2, 2.0$ and they add up to $431.2$. The variance is $431.2 \div 5 = 86.2$ and the standard deviation is $\sqrt{86.2} \approx 9.3$.

The mean is a little above the median because of the $92$.