Compound Interest-Chapter 9- Exercise 9(B)-Class 8

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Exercise 9 (B)

1. Calculate the amount and the compound interest by using the formula for compound interest.

 Q.N.

 Principal

 Rate Of interest

 Time (In years)

 1

 Rs 625

 4 %  p.a.

 2

2

 Rs 1000

 10 %  p.a.

 3

 3

 Rs 8000

 10 %  half-yearly

1.5


Q.1.Solution:

⇨ Given p=625 r=4 % n=2
⇨Then the annual Compound interest will be
        

⇨ Total Amount = P + C.I. = 625 + 51 =676 Rs

Q.2.Solution:
⇨ Given p=1000 r=10 % n=3
⇨ Then the annual Compound interest will be
      
⇨ Total Amount = P + C.I. = 1000 + 331 =1331 Rs

Q.3.Solution:
⇨ Given p=8000 r=10 % n=1.5 or 3/2
⇨ Then the Half-yearly Compound interest will be

        

⇨ Total Amount = P + C.I. = 8000 + 1261 =9261 Rs



Q.4. Reena and Ruchira borrowed Rs 60000 and Rs 50000 respectively for a period of 3 years. Reena paid simple interest at the rate of 10 % p.a., while Ruchira paid compound interest at the rate of 10 % p.a. Compounded annually.Who paid more interest and by how much ?

Solution:

⇨For Reena
⇨Given
⇨p = 60000
⇨r = 10 %
⇨n = 3 p.a.
⇨Therefore the Simple interest for Reena will be

        
 Rs

⇨For Ruchira
⇨Given
⇨p = 50000
⇨r = 10 %
⇨n = 3 p.a.
⇨Therefore the Compound interest for Ruchira will be

        
 Rs

⇨From above Reena paid more interest than Ruchira by
= Interest paid by Reena - Interest paid by Ruchira
= 18000 - 16550
= 1450 Rs


Q.5. Sangeeta lent Rs 40960 to Amar to purchase a shop at 12.5 % per annum. If the interest is compounded semi-annually, find the interest paid by Amar after 1.5 or 3/2 years ?

Solution:

⇨Given
⇨p=40960
⇨r=12.5 %
⇨n=1.5 or 3/2
⇨Then semi-annually Then the semi-annually Compound interest paid by Amar will be

      
 Rs

Q.6. Sudhir lent Rs 2000 at compound interest at 10 % payable yearly, While Prashant lent Rs 2000 at compound interest at 10 % payable half yearly. Find the difference in the interest received by Sudhir and Prashant at the end of one year?

Solution:

⇨In case of Sudhir
⇨Given
⇨p=2000
⇨r=10 %
⇨n=1 p.a.
⇨Then the annual Compound interest paid by Sudhir will be

        
 Rs
⇨In case of Prashant
⇨Given
⇨p=2000
⇨r=10 %
⇨n=1 Half-yearly.
⇨Then the half-yearly Compound interest paid by Prashant will be

        
 Rs

⇨Therefore The difference in the interest received by Sudhir and Prashant at the end of one year Will be
= 205 - 200
= 5 Rs



Q.7. Find the difference between simple interest and compound interest on Rs 16000 for 1.5 rears or 3/2 years at 5 % per annum ,compound interest being reckoned half yearly.

Solution:

⇨Given
⇨p=16000
⇨r=5 %
⇨n=1.5 annul for S.I.
⇨The simple interest will be

        
 Rs
⇨Given
⇨p=16000
⇨r=5 %
⇨n=1.5 Half-yearly for C.I
⇨The compound interest will be

        
  
  
 Rs

⇨Therefore the difference between S.I and C.I will be
= C.I - S.I.
=1230.25 - 1200
=30.25 Rs


Q.8. Find the compound interest on 3125 for 3 years if the rates of interest for first, second and third year are respectively 4%, 5%, 6%.

Solution:

⇨Given
⇨p=3125
⇨r1=4 %
⇨r2=5%
⇨r3=6%
⇨n=3 years
⇨For different rates on successive years, Total amount 'A' will be

      
 Rs
⇨Therefore The Compound interest will be
= A- P
=3617.25 - 3125
= 492.5 Rs

Q.9. A District contains 64000 inhabitants. If the population increases at the rate of 2.5 or 5/2 % per annum ,find the number of inhabitants at the end of 3 years.

Solution:

⇨Given
⇨p=64000
⇨r=2.5 %
⇨n=3
⇨The number of inhabitants at the end of 3 years

        
 Rs

Q.10. The nagar palika of certain city started campaign to kill the stray dogs which numbered 1250 in the city as a result, the population of stray dogs started decreasing at the rate of 20 % per month . Calculate the number of stray dogs in the city three months after the campaign started.

Solution:

⇨Given
⇨p=1250
⇨r=20% 
⇨n=3 months
⇨The number of stray dogs in the city three months after the campaign started Will be

        
 dogs
⇨Therefore  no. of stray dogs=640



Q.11. The value of a machine depreciates each year by 10  % of it's value at the beginning of that year. It' value when new is Rs 750, find it's value when it is 2 years old.

Solution:

⇨Given    
⇨p=750    
⇨r=10%     
⇨n=2 months
⇨The value of a machine when it is 2 years old will be
        
 Rs

Q.12. The national wealth of a country increases by 4% of it's value at the beginning of every year .Find the national wealth of the country in 1985, if it was estimated as Rs 3.125 x 10^12 in 1983.

Solution:

⇨Given    
⇨p=3.125 X 10^12   
⇨r=4%     
⇨n=2 years
⇨The national wealth of the country in 1984
        
 Rs
National wealth =3380 X 10^9 Rs

Q.13.The price of the scooter depreciates by 2% of it's at the beginning of each year. Find The sale value of the scooter after 3 years , if it's present sale value is Rs 12000.

Solution:

⇨Given    
⇨p=12000   
⇨r=2%     
⇨n=3 years
⇨The sale value of the scooter after 3 years will be
        
 Rs
⇨value of scooter=11294.304 Rs

Q.14. The population of Andhra Pradesh was 5.4 X 10^7 in 1988. If the population was growing at a constant rate of 2.4 % per annum .What was the population in 2008 A.D.[Given that (1.024)^20=1.60694].

Solution:

⇨Given    
⇨p=5.4 X 10^7     
⇨r=2.4%     
⇨n=2008 - 1988 =20 years
⇨The population in 2008 will be
        
 (approx)

Multiple Choice Questions


Q.15. A steno- typist deposits Rs 10000 in a bank for a period of 3 years at 12 % per annum compound interest . The interest accrued to her after maturity will be

Solution:

⇨Given    
⇨p=10000     
⇨r=12%     
⇨n=3 years
⇨The interest accrued to her after maturity will be
        
 Rs

Q.16. The present population  of a city is 180000. If it increases at the rate of 8% per annum , It's population after 2 years will be

Solution:

⇨Given
⇨p=180000     
⇨r=8%     
⇨n=2 years
⇨Population after 2 years will be
        

High Order Thinking

Q.17. Umesh set up a small factory by investing ₹40,000. During the first three successive years his profits were 5%,10% and 15% respectively. If each year the profit was on previous years' capital, calculate his total profit.

Solution:

⇨Given    
⇨p=40000     
⇨r1=5%  
⇨r2=10%    
⇨r3=15%
⇨Simple interest for 1st year will be
        
 Rs
⇨Total money invested in 2nd year=40000 + 2000 = 42000 Rs 
⇨A/Q 
Profit in 2nd year =10% 
Then Simple interest for 2nd year will be 
        
 Rs
⇨Total money invested in 3rd year 
= 42000 + 4200 
= 46200 Rs 
⇨Profit in 2nd year =15% 
Then Simple interest for 3rd year will be 
                 
 Rs
⇨Total Money After 3 years
= 46200 + 6930
= 53130 Rs
⇨Therefore total profit will be
= 53130 - 40000
= 13130 Rs

Q.18.The price value of the share of a company increase the the rate of 15% in the first year suffered a loss of 10% in the next year and again increased by 20% the third year if the percent value of a share is Rs 2000 what will be it's value after 3 years.

Solution:

⇨Given
⇨p=2000     
⇨r1=15% increase  
⇨r2=10% decrease    
⇨r3=20% increase  
⇨Simple interest  after 1 year will be
 
 Rs
⇨Share value after 1 year will be 
= 2000 + 300 
= 2300 Rs 
⇨Simple interest after 2nd year will be
 Rs
⇨Share value after 2nd year will be 
= 2300 - 230 
= 2070 Rs 
⇨Simple interest after 3rd year will be 
 Rs
⇨Share value after 2nd year will be 
= 2070 + 414 
= 2484 Rs

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