Compound interest

Q. The difference between the compound interest and simple interest on a certain sum at 10% p.a for 2 years is Rs. 631.Find the sum.

Ans. The formula is as under.


Sum = Diff X 100 X 100
                      r X r

Sum = 631 X 100 X100
               10 X 10  

Sum = 63100


The above formula can be used only for 2 years period.

The formula for 3 years will be


 Sum =  Diff X 100 X 100 X100
                  r X r X(300+r)



Q. The height of an equilateral triangle is    cm.Find it's area.

Ans. The formula is as under.


A =                   h is the height


A =    


A = 64



Q. A circle is inscribed in an equilateral triangle whose radius is   cm.
     What is the perimeter of the equilateral triangle?

Ans. The formula is as under.


The perimeter of an equilateral triangle = 3 X side
                                                                   = 3 X 2r X 
                                                                           = 3 X 2 X 4 X 

The perimeter of an equilateral triangle = 72

The side of an equilateral triangle  =  radius of circle X  
when the circle is inscribed in it