Question

a man invested 10000Rs and split into two schmes at annul rates of interest 8%&9% after one year he got 875Rs as interest from both . how much did he invested in each

Answer 1

Let’s start with a problem;

                                              There are 100 balls in a box, some black and some white; 10 more black than white. How many black, how many white?

  We can do this in several ways. Taking out 10 extra black balls for the time being, we have 90 left in the box, black and white are equal. So 45 of each. Adding the 10 black beads kept apart, black becomes 55 and white remains 45.

  We can do it with algebra also.(Recall the chapter Equations in class 8).

Taking the number of black balls as ‘ x’,the number of white balls is ‘ x-10 ‘ and since there are 100 in all,

                                                  x + (x-10) = 100

We can find out x from this;

                                                   2x – 10 = 100

                                                   2x = 100 +10

                                                  2x = 110

                                                     x = 55.

Thus we find the number of black balls as 55; subtracting 10, we get the number of white balls as 45.

There is another way of using algebra again. Taking number of black balls as ‘x’ and the number of white balls as ‘y’, we can write what we are told as two equations.

                                 x + y = 100

                                 x – y = 10