💰 Unit 7: Financial Mathematics
Perpetuity, Sinking Funds, EMI & Amortization, CAGR, Depreciation, Bond Valuation
Weightage: 10 Marks in Board ExamsTopics Covered in Unit 7
Master these 6 important topics
1. Perpetuity
Infinite series of equal payments, present value calculations
2. Sinking Funds
Accumulation of funds for future payments, periodic deposits
3. EMI & Amortization
Equated Monthly Installments, loan repayment schedules
4. CAGR
Compounded Annual Growth Rate for investments
5. Depreciation
Straight line and reducing balance methods
6. Valuation of Bonds
Present value, yield to maturity, bond pricing
Practice MCQs with Answers
Click "Show Answer" to reveal explanations
Formula: PV of Perpetuity = A/r
Where A = Annual payment = ₹1000, r = 8% = 0.08
PV = 1000/0.08 = ₹12,500
Sinking Fund Formula: A = S × r / ((1+r)ⁿ - 1)
S = ₹1,00,000, r = 0.10, n = 5
A = 1,00,000 × 0.10 / ((1.10)⁵ - 1)
A = 10,000 / (1.61051 - 1) = 10,000 / 0.61051 ≈ ₹16,380
The standard EMI formula is:
EMI = P × r × (1+r)ⁿ / ((1+r)ⁿ - 1)
Where P = Principal, r = monthly rate, n = number of months
Monthly rate = Annual rate / 12
= 12% / 12 = 1% = 0.01
CAGR = (Final Value/Initial Value)^(1/n) - 1
= (15,000/10,000)^(1/3) - 1
= (1.5)^(1/3) - 1
= 1.1447 - 1 = 0.1447 ≈ 14.5%
CAGR = (Ending Value / Beginning Value)^(1/n) - 1
Where n is the number of years
Annual Depreciation = (Cost - Salvage Value) / Useful Life
= (1,00,000 - 10,000) / 10
= 90,000 / 10 = ₹9,000
Book Value = Cost × (1 - r)ⁿ
= 50,000 × (1 - 0.10)²
= 50,000 × (0.90)²
= 50,000 × 0.81 = ₹40,500
64,000 = 80,000 × (1 - r)
1 - r = 64,000/80,000 = 0.80
r = 1 - 0.80 = 0.20 = 20%
When coupon rate (8%) < required return (10%), bond trades at discount.
When coupon rate > required return, bond trades at premium.
When coupon rate = required return, bond trades at par.
Annual Coupon Payment = Face Value × Coupon Rate
= 10,000 × 0.06 = ₹600
PV = A/r = 500/0.05 = ₹10,000
In amortization, as the outstanding principal reduces over time, the interest component decreases and the principal repayment component increases, while EMI remains constant.
FV = A × [((1+r)ⁿ - 1) / r]
= 10,000 × [((1.08)⁴ - 1) / 0.08]
= 10,000 × [(1.36049 - 1) / 0.08]
= 10,000 × 4.5061 = ₹45,061
Current Yield = Annual Coupon Payment / Current Market Price
It shows the annual return based on current market price.
Reducing balance method (WDV method) results in higher depreciation in early years as it applies a fixed percentage to the reducing book value, while straight line method gives constant depreciation.
CAGR (Compound Annual Growth Rate) smoothens out volatility and provides a single growth rate, making it ideal for comparing different investments over time.
Each EMI payment consists of two components: principal repayment and interest. The proportion changes over time with interest decreasing and principal increasing.
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Short Answer Questions with Step-by-Step Solutions
Practice 2-mark and 3-mark questions
(ii) Book Value after 3 years = ₹1,32,500
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Long Answer Questions with Complete Solutions
Practice 5-mark questions
(b) Balance after 3 years = ₹4,29,000
(b) Outstanding after 3 months = ₹4,64,830
Notice: Principal component increases while interest decreases
• SLM: Constant depreciation ₹54,000, final BV = ₹30,000
• RBM: Decreasing depreciation, final BV = ₹71,191
• RBM gives higher depreciation in early years
• SLM reaches exact salvage value
(b) Annual growth rates: 15%, 4.35%, 20.83%, 10.34%
(c) CAGR (12.46%) smoothens volatility and shows compound effect, while simple average (12.63%) treats each year equally without compounding. CAGR is better for comparing investments.
(b) PV of Face Value = ₹735.03
(c) Bond Price = ₹1,066.24
(d) Bond trades at PREMIUM because coupon rate (10%) > required return (8%), hence price (₹1,066.24) > face value (₹1,000)
(b) 20-year annuity PV = ₹98,181
(c) 50-year annuity PV = ₹1,22,335
Comment: As annuity period increases, its PV approaches perpetuity PV. The 50-year annuity (₹1,22,335) is 97.9% of perpetuity value (₹1,25,000), showing that distant cash flows have negligible present value.
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Case Study Based Questions
Real-world application problems
Home Loan Planning
Rajesh wants to buy a house worth ₹50,00,000. He has ₹10,00,000 as down payment and needs to take a loan for the remaining amount. The bank offers a home loan at 9% per annum for 20 years (240 months). He wants to understand his EMI obligations and loan repayment structure.
Loan Amount = House Value - Down Payment
= ₹50,00,000 - ₹10,00,000 = ₹40,00,000
Monthly rate = Annual rate / 12
= 9% / 12 = 0.75% = 0.0075
EMI = P × r × (1+r)ⁿ / ((1+r)ⁿ - 1)
P = ₹40,00,000, r = 0.0075, n = 240
(1.0075)²⁴⁰ = 6.0092
EMI = 40,00,000 × 0.0075 × 6.0092 / 5.0092
≈ ₹35,984
First month interest = Principal × Monthly rate
= ₹40,00,000 × 0.0075 = ₹30,000
Principal component = EMI - Interest
= ₹35,984 - ₹30,000 = ₹5,984
Investment and Asset Management
A company invested ₹20,00,000 in a business venture. After 4 years, the investment value grew to ₹28,00,000. Simultaneously, the company purchased machinery worth ₹15,00,000 which depreciates at 15% per annum using the reducing balance method.
CAGR = (Final/Initial)^(1/n) - 1
= (28,00,000/20,00,000)^(1/4) - 1
= (1.4)^0.25 - 1
= 1.0878 - 1 = 0.0878 ≈ 8.8%
Book Value = Cost × (1 - r)ⁿ
= 15,00,000 × (1 - 0.15)¹
= 15,00,000 × 0.85 = ₹12,75,000
Book Value = 15,00,000 × (0.85)⁴
= 15,00,000 × 0.52200625
= ₹7,82,063 (approximately)
Net Position = Investment Value + Machinery Value
= ₹28,00,000 + ₹7,82,063
= ₹35,82,063
Fixed Income Investment Portfolio
An investor is considering two investment options: Option A is a corporate bond with face value ₹10,000, coupon rate 12% per annum, 5 years to maturity, and market yield of 10%. Option B is a perpetual bond (console) paying ₹1,200 annually with the same market yield of 10%.
Annual Coupon = Face Value × Coupon Rate
= ₹10,000 × 12% = ₹1,200
Coupon Rate (12%) > Market Yield (10%)
When coupon rate exceeds market yield, bond trades at premium (above face value).
PV of Perpetuity = Annual Payment / Yield
= ₹1,200 / 0.10 = ₹12,000
New PV = 1,200 / 0.12 = ₹10,000
When market yield increases, bond/perpetuity value decreases (inverse relationship).
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