What is the average of all multiples of 10 from 2 to 198?

Key insight: the average of an arithmetic sequence equals the average of its first and last terms.

1. Identify the multiples of 10 between 2 and 198: they are 10, 20, 30, ..., 190.

2. Find the first term and the last term: first = 10, last = 190.

3. Compute the average using (first + last) / 2: (10 + 190) / 2 = 200 / 2 = 100.

4. Optional verification: count the terms. Number of terms n = (190 - 10) / 10 + 1 = 19. Sum = n * (first + last) / 2 = 19 * 200 / 2 = 19 * 100 = 1900. Average = sum / n = 1900 / 19 = 100.