To find the average of four tenths (0.4) and five thousandths (0.005), we first need to add these two numbers together and then divide the sum by 2.
Adding: 0.4 + 0.005 = 0.405
Now, we divide the sum by 2:
0.405 ÷ 2 = 0.2025
Therefore, the average of four tenths and five thousandths is 0.2025. The correct answer is option d: 0.2025.