Math Problem Statement

You have $400,000 saved for retirement. Your account earns 7% interest. How much will you be able to pull out each month, if you want to be able to take withdrawals for 15 years?

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Solution

To determine how much you can withdraw monthly for 15 years with a 7% annual interest rate, we use the present value of an annuity formula:

PV=PMT(1(1+r/n)nt)r/nPV = \frac{PMT \cdot (1 - (1 + r/n)^{-n \cdot t})}{r/n}

Where:

  • PVPV = present value ($400,000)
  • PMTPMT = monthly withdrawal (what we are solving for)
  • rr = annual interest rate (7% or 0.07)
  • nn = number of compounding periods per year (12 for monthly)
  • tt = number of years (15)

Rewriting to solve for PMTPMT: PMT=PV(r/n)1(1+r/n)ntPMT = \frac{PV \cdot (r/n)}{1 - (1 + r/n)^{-n \cdot t}}

Substituting values:

  • PV=400,000PV = 400,000
  • r=0.07r = 0.07
  • n=12n = 12
  • t=15t = 15

PMT=400,000(0.07/12)1(1+0.07/12)1215PMT = \frac{400,000 \cdot (0.07 / 12)}{1 - (1 + 0.07/12)^{-12 \cdot 15}}

Let me calculate this.# Given variables PV = 400000 # Present value r = 0.07 # Annual interest rate n = 12 # Compounding periods per year t = 15 # Number of years

Formula for PMT

PMT = (PV * (r / n)) / (1 - (1 + r / n) ** (-n * t)) PMT3595.31308340969963595.3130834096996successThe monthly withdrawal amount you can take for 15 years at a 7% annual interest rate is approximately $3,595.31.

Would you like a detailed explanation or further assistance with this calculation?

Here are 5 related questions you might find interesting:

  1. How would this change if you wanted to withdraw for 20 years instead of 15?
  2. What if the interest rate was 5% instead of 7%?
  3. How does compounding frequency (e.g., quarterly vs. monthly) affect the withdrawals?
  4. What if you want to leave a specific amount at the end of 15 years?
  5. How would inflation affect the value of these withdrawals over time?

Tip: When planning for retirement, always factor in inflation to preserve purchasing power over the years.

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Math Problem Analysis

Mathematical Concepts

Annuities
Compound Interest
Present Value

Formulas

Present Value of an Annuity formula: PV = (PMT * (1 - (1 + r/n)^(-n * t))) / (r/n)
Monthly Withdrawal formula (rearranged): PMT = (PV * (r/n)) / (1 - (1 + r/n)^(-n * t))

Theorems

Annuity Formula Theorem

Suitable Grade Level

Grades 11-12 and above (Financial Mathematics)