For successive increase/decrease in percentages, for successive years/times, the following formula will come handy:
Let the successive increase in percentages be a%a% and b%b%. In that case, the total increase will be (a+b+ab100)%(a+b+ab100)%
Lets try an example:
If the increase is 10% and 20 %, the successive increase will be (10+20+20∗10100)=32%(10+20+20∗10100)=32%.
If there`s an increase and a decrease, in that case, the decrease will be considered a negative value.
Lets try an example.
If there`s an increase of 20% and then a decrease of 10%, the successive percentage will be (20+(−10)+20∗(−10)100)=20−10−2=8%(20+(−10)+20∗(−10)100)=20−10−2=8% increase.
In case of discounts, the value of discount percentages will be considered negative.
Lets try an example:
If Kouton`s give 50% + 50% off on independence day, what is the final discount given by Koutons
The discount percentage will be (−50+(−50)+(−50)∗(−50)100)=−100+25=75%(−50+(−50)+(−50)∗(−50)100)=−100+25=75% discount.
This method is useful when the percentage increase / decrease if for lot many times. Once this method is mastered, successive percentage calculation will be a cakewalk and would relieve you of the pain of picking up pencil and scribing on paper.. :-)
Hope the methods helps you all.