Consider a mortgage with a balance of $250,000, that carries a 4% fixed-rate interest and has 20 years remaining to maturity. Would you benefit in any way from making an extra payment of $100 each month on the mortgage? Explain.

Present and future value calculations are dependent upon the interest rates used in the calculations. What does the interest rate represent, conceptually? I am not looking for a statistically or numerically-focused discussion here. Something more along the lines of what does it mean, economically, to say that the discount rate is 10% instead of 5%?