Question 26: The compound interest on a sum of money for years is and the simple interest on the same sum for the same period and at the same rate is . Find: (i) the rate of interest (ii) the sum.

Answer:

Compound Interest:

Principal , Rate of Interest per annum,

Compound Interest

… … … … … (i)

Simple Interest:

Principal , Rate of Interest annually, years

Interest

… … … … … (ii)

Now solving (i) and (ii) we get

$latex )

Question 27: Find the rate percent per annum if amounts to in years, interest being compounded half-yearly.

Answer:

Principal , Rate of Interest semi-annually, year

per annum

Question 28: Find the rate at which a sum of money will double itself in years if the interest is compounded annually.

Answer:

Principal , Rate of Interest annually, year

per annum

Question 29: Find the rate at which a sum of money will become four amount times the original in years if the interest is compounded half yearly.

Answer:

Principal , Rate of Interest annually, year

per annum

Question 30: A sum compounded annually becomes times of itself in years. Determine the rate of interest.

Answer:

Principal , Rate of Interest annually, year

per annum

Question 31: Rishi invested in a finance company and received after years. Find the rate of interest per annum compounded semi-annually.

Answer:

Principal , Rate of Interest semi-annually, year

per annum

Question 32: In how much time would amounts to at per annum compound interest?

Answer:

Principal , Rate of Interest annually, year

Question 33: In what time will become at per annum interest compounded half-yearly?

Answer:

Principal , Rate of Interest annually, year

Question 34: The compound interest, calculated yearly, on a certain sum of money for the second year is and for the third year is . Calculate the rate of interest and the original sum of money.

Answer:

Principal , Rate of Interest per annum,

… … … … (i)

Principal , Rate of Interest per annum,

… … … … (ii)

Principal , Rate of Interest per annum,

… … … … (iii)

Given: and

Therefore

… … … … (iv)

… … … … (v)

Dividing (v) by (iv) we get

Substituting in (iv)

Question 35: On what sum of money will the difference between the compound interest and simple interest for years be equal to , if the rate of interest charged for both is per annum?

Answer:

Compound Interest:

Principal , Rate of Interest per annum,

Compound Interest

Simple Interest:

Principal , Rate of Interest annually, years

Interest

Given:

Question 36: Mr Kumar borrowed for two years. The rate of interest for the two successive years are and respectively. If he repays at the end of the first year, find the outstanding amount at the end of second year.

Answer:

For the : We have,

Principal , Rate of Interest per annum,

Therefore

Therefore, the Amount at the end of

For the : We have,

Principal , Rate of Interest per annum,

Therefore

Therefore, the Amount at the end of year

Depreciation Problems

Question 37: The value of a machine depreciates at the rate of per annum. what will be its value years hence if the present value is ? Also, find the total depreciation during this period.

Answer:

Present Value Rate of Depreciation No of Years

Total depreciation

Question 38: Pritam bought a plot of land for . Its value is increasing by of its previous value after every six months. What will be the value of the plot after years?

Answer:

Present Value , Rate of Interest half yearly ,

Question 39: The value of a machine depreciates at the rate of per annum. It was purchased years ago. If its present value is , find its purchase price.

Answer:

Present Value Rate of Depreciation No of Years Value 3 years back

Total depreciation

Question 40: The cost of a T.V. set was quoted at the beginning of 1999. In the beginning of 2000 the price was hiked by . Because of decrease in demand the cost was reduced by in the beginning of 2001. What was the cost of the T.V. set in 2001?

Answer:

Cost of TV at the beginning of 1999

Cost of TV at the beginning of 2000

Cost of TV at the beginning of 2001

Question 41: Ashish staffed the business with an initial investment of . In the first he incurred a loss of . However, during the second year he earned a profit of which in third year rose to . Calculate the net profit for the entire period of years.

Answer:

Initial Investment at the beginning of 1st Year

Capital at the beginning of 2nd Year

Capital at the beginning of 3rd Year

Capital at the beginning of 4th Year

Net profit

Population Questions

Question 42: The present population of a town is . If it increases at the rate of per annum, what will be its population after years?

Answer:

Population , Rate per annum, years

Population after years

Population after years

Question 43: The present population of a town is . It grows at first and during year, second year and third year respectively. Find lts population after years.

Answer:

Current Population , Rate per annum, years

Population after

Population after

Question 44: There is a continuous growth in population of a village at the rate of per annum. If its present population is , what was it years ago?

Answer:

Population 3 years ago Current Population , Rate per annum, years

Therefore

Question 45: In a factory the production of scooters rose to from in years. Find the annual rate of growth of the production of scooters.

Answer:

Question 46: The population of a town increases at the rate of per thousand. Its population after years will be . Find its present population.

Answer:

Rate of Increase (population in 2 years) (Initial population)

Question 47: The count of bacteria in a culture grows by in the first hour, decreases by in the second hour and again increase by in third hour. If the count of bacteria in the sample , what will be the count of bacteria after hour.

Answer:

Current bacteria Population , Rate per annum, hours

Bacteria Population after

Bacteria Population after

Question 48: workers were employed to construct a river bridge in four years. At the end First year, workers were retrenched. At the second year of those working at that time were retrenched. However, to complete the project in time, the number of workers was increased by the end of the third year. How many workers were working during the fourth year?

Answer:

Current worker Population , Rate per annum, years

Worker Population after

Worker Population after

Question 49: A man started a factory with an initial investment of . In the first year, he incurred a loss of . However, during the second year; he earned a profit of which in the third year rose to . Calculate the profit for the entire period of three years.

Answer:

Initial Investment , Rate per annum, years

Worker Population after

Worker Population after

Therefore net profit

Question 50: The population of a city increases each year by of what it had been at the beginning of each year. If the population in 1999 had been , find the population of the city in (i) 2001 (ii) 1997.

Answer: