Understanding the Mathematics of Personal Finance

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Preface     ix

 

 

 

 

List of Abbreviations     iv

 

 

 

 

1.  Background Mathematics

1

 

1.1

Arithmetic Notation and Formulas     1

 

 

1.2

Minus (Negative) Signs     5

 

 

1.3

Lists and Subscripted Variables     6

 

 

1.4

Changes     9

 

 

1.5

Exponents     11

 

 

1.6

Summations     12

 

 

1.7

Graphs and Charts     13

 

 

1.8

Approximations     18

 

 

1.9

Rates - Average and Instantaneous     19

 

 

1.10

Inequalities and Ranges of Numbers     22

 

 

Problems     23

 

 

 

 

 

2.  Compound Interest

26

 

2.1

Some Mathematics     30

 

 

2.2

My Website Spreadsheet     31

 

 

2.3

Online Calculators     32

 

 

2.4

Scaling     32

 

 

2.5

Proration - Working Inside a Compounding Interval     33

 

 

2.6

Initial Charges and Effective Interest Rate     34

 

 

2.7

In the Limit - Continuous Compounding

 

 

Problems     37

 

 

 

 

 

3.  Loan Amortization and Savings

38

 

3.1

Loans     38

 

 

3.2

Calculating the Payment Amount     44

 

 

3.3

Paying Off a Loan Very Slowly     45

 

 

3.4

My Website Spreadsheet     46

 

 

3.5

A Note About Total Interest For a Year     47

 

 

3.6

OnLine Calculators     48

 

 

3.7

Loans With First Payment Due Immediately     48

 

 

3.8

Irregular Payments     49

 

 

3.9

Regular Savings     50

 

 

Problems     52

 

 

 

 

 

4.  Mortgages

54

 

4.1

OnLine Calculators     55

 

 

4.2

Fixed Rate Mortgages     55

 

 

4.3

Adjustable Rate Mortgages (ARMs)     57

 

 

4.4

Balloon Loans     59

 

 

4.5

Up-Front Costs     59

 

 

Problems     60

 

 

 

 

 

5.  Prepayment Penalties

61

 

5.1

Rule of 78     63

 

 

5.2

Other Prepayment Penalties     66

 

 

Problems     68

 

 

 

 

 

6.  Credit Cards

70

 

6.1

Credit Card Statements     70

 

 

6.2

Transfers     73

 

 

6.3

Payment Allocation     75

 

 

6.4

Daily Balance     76

 

 

6.5

Some Calculation Examples     76

 

 

6.6

Grace Period     81

 

 

6.7

Changing Interest Rates     81

 

 

6.8

A Bankruptcy Spiral      81

 

 

6.9

Minimum Payment     83

 

 

6.10

Other Interest Calculation Approaches     83

 

 

6.11

Debit Cards - Something Completely Different     83

 

 

Problems  84

 

 

 

 

 

7.  Present Value

86

 

7.1

Online Calculators     88

 

 

7.2

Doing It With My Spreadsheet     88

 

 

7.3

The Effect of Interest Rates On Present Value Calculations     90

 

 

7.4

Why This All Matters     91

 

 

7.5

A Very Involved Example: Writing Your Own Spreadsheet     91

 

 

7.6

Future Value     93

 

 

7.7

Present Value of Prepayment Penalties     94

 

 

Problems     95

 

 

 

 

 

8.  Comparing Loans

96

 

8.1

Up-Front Costs     99

 

 

8.2

Adjustable Rate Mortgages (ARMs)     100

 

 

8.3

A Few Last Words     102

 

 

Problems     103

 

 

 

 

 

9.  Taxation and Inflation

105

 

9.1

Understanding Personal Federal Income Tax Rates     105

 

 

9.2

Online Tax Calculators     111

 

 

9.3

Taxation of Earned Interest 111

 

 

9.4

Deductible Interest     112

 

 

9.5

Deferred Taxation Savings     112

 

 

9.6

Online Deferred Taxation Plan Calculators     115

 

 

9.7

Inflation     115

 

 

Problems     118

 

 

 

 

 

10.  Life Insurance

119

 

10.1

What Is An Insurance Policy?     119

 

 

10.2

Probability     120

 

 

10.3

Introduction to the Life Tables     126

 

 

10.4

Expected Value     128

 

 

10.5

Term Insurance     130

 

 

10.6

Time Payments     133

 

 

10.7

Decreasing Term Insurance     134

 

 

10.8

Insurance for the Rest of Your Life     134

 

 

10.9

Whole Life Insurance     136

 

 

10.10

Breaking Down the Year     139

 

 

Problems     142

 

 

 

 

 

11.  Annuities

144

 

11.1

A Benchmark Savings Plan     145

 

 

11.2

Immediate Annuity With Period Certain     145

 

 

11.3

Deferred Annuities     148

 

 

11.4

Life Annuities     150

 

 

11.5

Payments for Couples     153

 

 

11.6

Online Calculators     156

 

 

11.7

Variable Annuities     156

 

 

Problems     157

 

 

 

 

 

12.  Reverse Mortgages and Viatical Settlements

158

 

12.1

Reverse Mortgages     158

 

 

12.2

Viatical Settlements     162

 

 

Problems     163

 

 

 

 

 

13.  Investing:  Risk versus Reward

164

 

13.1

Stocks     165

 

 

13.2

Portfolios     167

 

 

13.3

Calculators     171

 

 

13.4

Dollar Cost Averaging     173

 

 

13.5

Short Sales     174

 

 

13.6

Stock Dividends     174

 

 

13.7

Bonds     175

 

 

13.8

Options     175

 

 

13.9

Online Calculators and Listings     179

 

 

13.10

Ponzi Schemes and Other Scams     180

 

 

Problems      185

 

 

Reference     186

 

 

 

 

 

14.  Gambling

187

 

14.1

Probability and Odds     187

 

 

14.2

Probability and Expected Return     188

 

 

14.3

Pari-Mutuel Betting    193

 

 

Problems     197

 

 

 

 

 

15.  Spreadsheet Calculators

198

 

15.1

Introduction to the Spreadsheets     198

 

 

15.2

Some Programming Notes     202

 

 

 

 

 

16.  Solutions

207

 

16.1

Chapter 1     207

 

 

16.2

Chapter 2     210

 

 

16.3

Chapter 3     213

 

 

16.4

Chapter 4     215

 

 

16.5

Chapter 5     216

 

 

16.6

Chapter 6     218

 

 

16.7

Chapter 7     220

 

 

16.8

Chapter 8     221

 

 

16.9

Chapter 9     223

 

 

16.10

Chapter 10     226

 

 

16.11

Chapter 11     229

 

 

16.12

Chapter 12     233

 

 

16.13

Chapter 13     234

 

 

16.14

Chapter 14     237

 

 

 

 

 

Index     240

 

 

 

 

 

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