Explanation:

- To find the average of the first 50 positive even numbers, note that the first even number is 2 and the 50th is 100 (i.e., 2, 4, 6, ..., 100).

- The sum of an arithmetic sequence is given by: \((\text{Number of terms}/2) \times (\text{First term} + \text{Last term})\).

- The sum of these numbers is: \((50/2) \times (2 + 100) = 25 \times 102 = 2550\).

- The average is the sum divided by the number of terms: \(2550/50 = 51\).

Option 3: 51 - This is the correct average.

Option 1: 50.5 - Incorrect as it's lesser than the actual average.

Option 2: 50 - Incorrect for being an even number average oversight.

Option 4: 51.5 - Incorrect as it's greater than the calculated average.