Answer:
Invest at a minimum of 7.5% annual simple interest
Explanation:
Given the goal of purchasing a boat that will cost $30,000 in 20 years, David needs to earn an interest computed below on his investment in the savings account.
Interest required = 30,000 - 12,000
= 18,000
Therefore the minimum rate of interest that will achieve this goal,
= Principal * rate * time = target amount
= 12,000 * R * 20 years = 18,000
= R = 18,000/(12,000*20) = 0.075 = 7.5%.
In addition, David could also continue his saving from his teaching job. This will reduce the minimum investment return required to achieve the goal.
