Interest Calculations
1. Calculate Simple Interest (SI) on 5,000 for 3 years at 6% p.a.
SI formula: $$SI = \frac{P \times R \times T}{100}$$
Given: $$P = 5000, R = 6, T = 3$$
Calculate:
$$SI = \frac{5000 \times 6 \times 3}{100} = 900$$
2. Find Compound Interest (CI) on 8,000 for 2 years at 5% compounded annually.
CI formula: $$A = P\left(1 + \frac{R}{100}\right)^T$$
CI = Amount - Principal
Given: $$P = 8000, R = 5, T = 2$$
Calculate Amount:
$$A = 8000 \times \left(1 + \frac{5}{100}\right)^2 = 8000 \times 1.1025 = 8820$$
CI:
$$CI = 8820 - 8000 = 820$$
3. A bill of 60,000 is discounted at 6% p.a. for 3 months before maturity. Find discount.
Discount formula:
$$D = \frac{P \times R \times T}{100}$$
Convert time to years:
$$T = \frac{3}{12} = 0.25$$
Calculate:
$$D = \frac{60000 \times 6 \times 0.25}{100} = 900$$
4. Find present value of 10,000 due in 4 years at 7% p.a. SI.
Present Value formula:
$$PV = \frac{FV}{1 + \frac{R \times T}{100}}$$
Given: $$FV = 10000, R = 7, T = 4$$
Calculate:
$$PV = \frac{10000}{1 + \frac{7 \times 4}{100}} = \frac{10000}{1 + 0.28} = \frac{10000}{1.28} = 7812.50$$
5. What sum amounts to 6,720 in 2 years at 8% p.a. CI?
Amount formula:
$$A = P \left(1 + \frac{R}{100}\right)^T$$
Given $$A=6720, R=8, T=2$$
Find $$P$$:
$$P = \frac{A}{(1 + \frac{R}{100})^T} = \frac{6720}{(1.08)^2} = \frac{6720}{1.1664} = 5760$$
6. What annual payment will discharge a debt of 12,000 due in 3 years at 10% p.a.?
This is an installment or annuity problem.
Using formula for Present Value of an annuity:
$$PV = P \times \frac{1 - (1 + r)^{-n}}{r}$$
Where:
$$PV = 12000, r = 0.10, n = 3$$
Solve for $$P$$ (annual payment):
$$12000 = P \times \frac{1 - (1 + 0.10)^{-3}}{0.10} = P \times 2.48685$$
$$P = \frac{12000}{2.48685} = 4825.41$$
7. Calculate the amount due if 1,200 grows at CI 12% p.a. for 3 years.
$$A = P \times (1 + \frac{R}{100})^T = 1200 \times (1.12)^3 = 1200 \times 1.404928 = 1685.91$$
8. How much should be invested to get 20,000 after 5 years at 6% CI?
Find Principal $$P$$ using:
$$A = P \times (1 + \frac{R}{100})^T$$
Given $$A=20000, R=6, T=5$$
Calculate:
$$P = \frac{20000}{(1.06)^5} = \frac{20000}{1.3382255776} = 14937.42$$