[tex]\\ \text{On his last four tests, Danilo scored }55\%, \ 78\%, \ 84\% \text{ and }93\%\\ \text{Let the score in the next test is x percent.}\\ \\ \text{now given that the average of all five tests is }80\%\\ \\ \text{so we have}\\ \\ \frac{55+78+84+93+x}{5}=80\\ \\ \Rightarrow \frac{310+x}{5}=80\\ \\ \text{now on cross multiplying, we get}\\ \\ 310+x=80\times 5\\ \\ \Rightarrow 310+x=400\\ \\ \Rightarrow x=400-310\\ \\ \Rightarrow x=90[/tex]
Hence Danilo should score 90 % in the fifth test to get an average of 80%
