1. PSAT MATHEMATICS 9-E Averages

2. Average The average of n numbers is the sum of those numbers divided by n.

3. Example The average (arithmetic mean) of Carol’s grades on the 6 French tests that she has taken this year is 86. If her average after the first 4 tests was 83, what was the average of her fifth and sixth tests? A. 84.5 B. 87.5 C. 89 D. 90 E. 92

4. Deviation The difference between each number in a set and the average of those numbers.

5. Example In Mr. Walsh’s biology class, the average (arithmetic mean) of the grades earned by the 15 girls was 90, and the average grade earned by the 10 boys was 80. What was the class average?

6. Example In 1998, Judith sold 9 paintings. The selling prices were $500, $1100, $2000, $500, $1200, $5000, $700, $500, and $4000. What is the average (arithmetic mean) of the median and mode of this set of data?

7. Practice Problems