The document discusses calculations related to simple and compound interest, presenting several problems and their solutions involving sums of money, interest rates, and time periods. It includes examples to find principal amounts, rates of interest, and compound interest over specified durations. Key concepts such as the difference between simple and compound interest and formulas for their calculations are also outlined.

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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