Answer: 7.1 years
Step-by-step explanation:
Lets write a simple interest expression for this:
SI = P(1 + rt)
10,000 = 1,000(1 + 0.065[t])
This model is not quite complete yet, since he is adding 1200 every year. To fix this, we simply add a constant term, 1200t, where t is the number of years that have passed.
10,000 = 1,000(1 + 0.065[t]) + 1200t
Now we just need to evaluate this:
10,000 = 1,000 + 65t + 1200t
9,000 = 1265t
.: t ≅ 7.115
It will take about 7.1 years
