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1. Simple Interest
and
Compound Interest

2. 1. A certain sum of money borrowed at a certain rate of interest in SI
amounts to 6900/- in 3 years and 8100 in 7 years. Find the sum and rate
of interest?
2. A certain sum of money borrowed at a certain rate of interest in SI, triples
itself in 8 years. In how many years will the same become 6 times itself at
the same rate of interest ?
3. Find the compound interest on a sum of 20,000/- at the rate of 20% per
annum for 2 years interest being calculated for every 6 months?
4. The SI and CI on a particular sum of money for 2 years at a certain rate of
interest is 1600/- and 1664/- respectively. Find the sum and ROI?
5. The difference between SI and CI on a particular sum of money at the rate
of 5% per annum for 2 years is 40/-. Find the sum?

3. SI = Amount = Principal + interest
• The interest for any year will be calculated on the principal (Sum
borrowed or lent)
• On a particular sum of money at a certain rate of interest. The SI
for any year will be same
• Suppose if P=1000, ROI = 10% , Term = 3 years
SI CI
Interest Amount Interest Amount
100 1100 100 1100
100 1200 110 1210
100 1300 121 1331
1st
2nd
3rd
Basics :

4. • A = P(1 + ) CI = Amount - Principal
n = number of times interest to be calculated
• In CI, the interest for any year will be calculated on the amount to
be paid except the first year which is calculated in principal (Interest
calculated annually)
• On a particular sum of money at a certain rate of interest, the SI
and CI for the 1st year will be same
• CI of (n+1)th year = CI of nth year + R% of CI of nth year
• First year interest = R% of principal ( For both SI and CI, interest
calculated annually)

5. A certain sum of money borrowed at a certain rate of interest in SI
amounts to 6900/- in 3 years and 8100 in 7 years. Find the sum and rate
of interest?
Ans :
A3 = P + 3I = 6900
A7 = P + 7I = 8100 => I = 300 and P = 6000
Principal = 6000
Rate of Interest =
Therefore Rate of interest =
1.
Sum = 6000 and Rate of interest = 5%

6. A certain sum of money borrowed at a certain rate of interest in SI,
triples itself in 8 years. In how many years will the same become 6 times
itself at the same rate of interest ?
2.
Time Period = 20 years
Ans :
Let P = 100
 Amount = 300 and Interest = 200 for T = 8 years ( Amount triples itself )
 For Amount = 600 Term = ?
 Interest = 500
Therefore SI = => Interest Term
=> = => => x = 20 years
200 – 8
500 – 20

7. Find the compound interest on a sum of 20,000/- at the rate of 20% per
annum for 2 years interest being calculated for every 6 months?
3.
Ans :
A = P(1 + ) CI = Amount - Principal
 A = 20000 (1 + ) For 2 years n = 4
 A = 29282/-
 CI = Amount - Principal
= 29282 – 20000
= 9282/-
Compound Interest = 9282/-
20000( at 10%) = 2000
2000 + 200 = 2200
2200 + 220 = 2420
2420 + 242 = 2662
total = 9282

8. The SI and CI on a particular sum of money for 2 years at a certain rate
of interest is 1600/- and 1664/- respectively. Find the sum and ROI?
4.
Ans :
Sum = 10000 and ROI = 8%
1600 1664
SI CI
1ST 800 800
2ND 800 864
Rate of Interest =
Rate of interest =
= 8 %
 For 100rs - Interest 8/-
 For ? Rs – Interest 800/-
 Sum = 10000
 ROI = 8%
100 – 8
10000 – 800

9. The difference between SI and CI on a particular sum of money at the
rate of 5% per annum for 2 years is 40/-. Find the sum?
5.
Ans :
5 % of 1st year = 40
100% of 1st year = ? (800)
Similarly
5% of P = 800
100% of P = 16000
Therefore Sum = 16000/-
Sum = 16000/-

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Problems for practice are given in the description of the video.

11. Practice problems
on SI and CI

12. 1. The si and ci on a particular sum of money at a certain rate of interest for 2
years is 840/- and 861/- respectively. Find the rate of interest?

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