Question

In Chemistry class, Andrew has earned scores of 64, 69, and 73 on three tests. He must maintain an average of 70 to pass the course. What score must Andrew earn on the final exam to pass the course?

Answer 1

X - the score he must earn
The average of n numbers is the sum of these numbers divided by n.

$\frac{64+69+73+x}{4}=70 \\ \frac{206+x}{4}=70 \ \ \ \ \ \ \ \ \ \ \ \ |\times 4 \\ 206+x=280 \ \ \ \ \ \ \ \ |-206 \\ x=74$

He must earn a score of (at least) 74.