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SAI International School
                                                        CLASS - VIII

                  Mathematics
                  CHAPTER-8: Comparing Quantities             Lesson Notes





                  SUBTOPICS:  Application of CompoundInterest

                  Applications of Compound Interest Formula:
                  There are many practical situations where we are in need to calculate CI. Some of the
                  examples are given:
                  (i) The rate of population growth.(Increase or decrease in Population)
                  (ii) The rate of growth of bacteria. ( when rate of growth is known)
                  (iii) The increment or decrement/ depreciation/ in price of certain items.( house,
                  machine,vehicles)

                  Example: The population of a town  was 176400 in the year 2015, It increases at the
                  rate of 5% per annum. What would be its population in the year 2017?
                  SOLUTION:
                  Population in the year 2015= 176400
                  Rate of increase= 5% per annum
                  Population in the year 2017 = Population after 2 years

                                   5
                                      2
                  {176400 × (1 +     ) }
                                  100
                                21
                  ={176400 × ( ) }
                                   2
                                20
                  = 194481
                  Hence the population of the town would be 194481.

                  Example:The  Population of a town 2 years ago was 62500. Due to migration to cities it
                  decreases every year at the rate of 4% per annum. Find the present population.

                  Solution:Population 2 years ago=62500, Rate of decrease= 4% per annum
                                                     4
                                                        2
                  Present Population= 62500(1 −        )
                                                    100
                                        = 62500( 24  ×  24 )= 57600
                                          25   25

                  Hence the present population of the town is 57600.
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