1. The document provides examples of calculating simple interest using the formula: Interest = Principal x Rate x Time. It shows how to calculate simple interest for problems involving different time periods, interest rates, principal amounts and determining unknown values. 2. It also introduces the concept of compound interest and shows one example of calculating compound interest over 3 years at 10% interest. 3. Additionally, it explains how to calculate the number of years for a principal sum to double at a given interest rate compounded annually, and provides one problem working through this calculation at 4% interest.

2. P= Principal
N= Number of years
R= Rate of interest
Amount= Principal+Simple Interest
S.I = Pni
i= r/100
Amount= P+Pni or P (1+ni)
Simple Interest (SI)

3. 1. What is the simple interest earned from the
principal of Rs.6000 at 15%interest p.a in 2
years?
Given:
Principal= Rs.6000
N= 2 years
R= 15%
Simple interest= PNR/100
 6000*2*15/100
 Rs.1800
Amount= Principal + SI
 6000 + 1800
 Rs. 7800

4. 2. Find the amount and simple interest for
Rs.5000 10% p.a for 3 years?
Given:
Principals = Rs.5000
Rate = 10% pa
N =3 years
Simple interest= PNR/100
 5000*3*10/100
 Rs.1500
Amount= Principal + SI
 5000 + 1500
 Rs. 6500

5. 3. Calculate the total interest on Rs.500 for73
days, Rs.720 for 14 weeks and Rs.900 for 3
months at 6 %.
Given:
(i) Principal = Rs.500, n= 73/365, r= 6/100
(ii) Principal = Rs.720, n= 14/52, r= 6/100
(iii) Principal = Rs.900, n= 3/12, r= 6/100
Solution:
(i)S.I=PNR/100(500*6*73)/(100*365) Rs.6
(ii)S.I=PNR/100(720*6*14)/(100*52)
Rs.11.63
(i)S.I=PNR/100(900*6*3)/(100*12)
Rs.13.5
Total interest= rs.( 6+11.63+ 13.5)
Rs.31.13

6. 4. Find the principal sum which yields simple
interest of rs.77 in 8 years at 3.5% pa?
Given
Principal = ?
R = 3.5%
N = 8 years
S.I = Rs.77
S.I = PNR/100
77 = P * 3.5 * 8/ 100
77*100 = 3.5 * 8 * P
7700 = 28 * P
P = 7700/28
Principal = Rs.275

7. 5. What sum of money invested at 10%pa in
Simple interest will amount to Rs.1200 in 2 years?
Given:
Principal = ?
R = 10%
N = 2 years
Amount = Rs.1200
A= P (1+ni)
1200= P (1+ 10*2/100)
1200 = P (6/5)
P = 1200 * 5 / 6
Principal = Rs.1000

8. 6. Find the period of which a sum of Rs.1200 will
amount to rs.1700 at 12%pa ?
Given:
Principal = Rs.1200
R = 12%
N = ?
Amount = Rs.1700
S.I = Amount- Principal
 1700-1200
 Rs. 500
S.I = PNR/100
500= (1200 *12* N)/100
500*100 = 1200*12*N
N = 500*100/1200*12
N = 500/12* 12
N = 3.47 years

9. 7. Find the rate of interest p.a if the Simple
interest on a principal of Rs.5000 is Rs.800 for 4
years.
Given
Principal = Rs.5000
R = ?
N = 4 years
S.I = Rs.800
S.I = PNR/100
800 = 5000 * 4 * R / 100
800 * 100 = 20000 * R
80000 = 20000 * R
R = 80000/20000
R = 4 %

10. 8. What time will a sum of money double itself at
10%pa in Simple interest.
Solution:
Let Principal be Rs.100
Amount double of principal Rs.200
S.I  Amount – Principal
= 200-100  Rs.100
R = 10%
N = ?
S.I = PNR/100
100 = 100 * N * 10 /100
10N = 100
N = 100/10
Number of years = 10years

11. 9. What time will a sum of money triple itself at
10%pa in Simple interest.
Solution:
Let Principal be Rs.100
Amount triple of principal Rs.300
S.I  Amount – Principal
= 300-100  Rs.200
R = 10%
N = ?
S.I = PNR/100
200 = 100 * N * 10 /100
10N = 200
N = 200/10
Number of years = 20 years

12. 10. A sum of money amounted to Rs.1,071 in 6 months
and Rs.1,106 in 16 months, calculate the rate of Simple
Interest.
Solution:
Amount = Rs.1,1071 in 6 months
Rs.1,106 in 16 months
A= P (1+ni)
1071 = P ( 1+(6/12)i)
1106 = P ( 1+(16/12)i)
1071 * 12 = P (12 + 6i)  12852 =P (12 + 6i)–(1)
 P = 12852/(12 +6i)
1106 * 12 = P(12 + 16i)13272 =P(12 + 16i) - (2)
P = 12852/(12 +6i) substitute in (1)
i= 5040/126000
i = 0.04
R= 0.04*100
R=4%

13. Compound Interest

14. 1. Find the compound interest, if the principal
Rs.6000, rate of interest is 10% pa in 3 years.
Solution

15. 2. Find the number of years in which a sum of
money will double it self at 4% pa in compound
interest.
Solution

16. 3. The difference between SI and CI is Rs,121.
number of years is 5 and the rate of interest is
8%. Find out the Sum?
Solution

17. 4. What rate of interest is denoted by 6% pa,
payable quarterly? - Effective rate of interest