Answer
86%
Work Step by Step
The average of the exams is:
Average score: $\frac{82+75+71+2*final}{5}$
Where $final$ is her final score. We multiply by 2 because the final score counts twice and we divide by $5$ because the final adds 2 more test scores to the previous 3. The average score needs to be 80:
$80=\frac{82+75+71+2*final}{5}$
We solve for the final score:
$final=\frac{80*5-(82+75+71)}{2}=86$
Thus her final score needs to be over 86% for Linh to get 80% is the class.
