Solution
Given that the mean score after 6 biology tests is 79.,
That means the total score is 6 × 79 = 474
For Ruben to have a new average of 81, that means
[tex]\begin{gathered} \frac{474+x}{6+1}=81 \\ \\ \Rightarrow\frac{474+x}{7}=81 \\ \\ \Rightarrow474+x=567 \\ \\ \Rightarrow x=567-474 \\ \\ \Rightarrow x=93 \end{gathered}[/tex]Therefore, Ruben need to score 93 on the next test to raise his average (mean) to 81
