## College Algebra 7th Edition

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.