suppose, you have $20,000 in your account. you receive a monthly
interest of $200 for that money. you also could have invested that money
and got a return of monthly $500 from that investment. however, now
you used the money to decorate your house. what is your opportunity
cost in this case?

According to the data provided the opportunity costs is detailed below:

Initial Balance  $20,000

Monthly interst      $200

Investment             $500

The Opportunity cost is $500

Explanation:

The opportunity cost is the price you pay for not choosing best second alternative when you make a decision. In this case the person has three options:

1.Spending the money  

2.Save the money

3.     Invest the money

Once the money is spent the opportunity costs is generated and it is measured by the interest rate lost for not keeping the money in the investment that will generate an interest rate of $500 monthly.

answer; the above statement is (true);