Increase and decrease concept
Problem 1: If the radius of the right circular cylinder is increased by 40% and its height is reduced by 37.5% then find the percentage change in its volume?
Solution: Radius increased to 40% =
Height decreased to 37.5%=
Volume of a cylinder =
Actual volume =
Height decreased = 8-3 =5
% change in its volume =
Problem 2: If the length of the rectangle is increased by 20% and the breadth of the rectangle is decreased by 20% find the percentage change in its area?
Solution: Length increased to 20%
Breadth decreased to 20%
Area of the rectangle = Length * Breadth
Actual area = 10*10 = 100
Changed area = 12*8 =96
% change in the area =
Here ‘-‘ indicates area decreased to 4%
Shortcut method: Direct formula = = 4
- The above method is applicable when there is increase or decrease in the value of 10%,20%,30,%40%,50%,60%, etc.
- If such values occur follow first problem method. It is not applicable when the fractional values occur.
- The fractional values like 37.5%,%, etc., If such values occur follow first problem method.