Final answer:
The value of the investor's portfolio one year ago was $130,000.
Step-by-step explanation:
To find the value of the portfolio one year ago, we can use the concept of doubling. If the portfolio has doubled in value over the last 12 months and is currently worth $260,000, we can divide the current value by 2 to find the value one year ago.
So, $260,000 / 2 = $130,000
Therefore, the value of the portfolio one year ago was $130,000.