The table shows quarterly sales for product X: Q1 120, Q2 150, Q3 180, Q4 210. What is the average quarterly sales?

• A. 150
• B. 165
• C. 180
• D. 210

Answer: (B)

The average is found by adding all values and dividing by how many there are. For 120, 150, 180, and 210, the sum is 660, and dividing by 4 gives 165. Because the quarterly sales rise by a constant amount (an arithmetic sequence), the average also equals the midpoint of the first and last values: (120 + 210) / 2 = 165. So the average quarterly sales is 165.