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All About Percentages
The detail concepts of the Percentage is collected from various source. I guess it will useful for others.
What is a Percentage?
A fraction with denominator 100 is called percentage. To convert a fraction into percentage, multiply by 100 and put % sign.
Expressing one quantity as percentage of other:
Ex: What percent is number 5 of number 25?
Out of 25-> 5,
Out of 1-> 5/25,
Out of 100-> (5/25)*100= 20%.
Percentage Change:
General Formula: Percent change=\(((Change in Quantity)/(Original Quantity)*100)\)
Percentage increase=\((Increased value-original value)/(Original value)*100\)
Percentage decreased=\((Original value-Decreased value)/(Original value)*100\)
Percentage Change Advance:
If a value R is increased by x%, then decrease the increased resultant value \((R+Rx/100)\) by \((x/(x+100)*100)%\) to get back the original value R.
If a value R is decreased by x%, then increase the decreased resultant value\( (R-Rx/100)\) by\( (x/(100-x)*100)%\) to get back the original value R.
Ex: 1000 is increased by 20% then resultant value is 1200.
20/120*100=16.67% (Rounded to nearest digit)
So, 1200 is reduced by 16.66% = 1200*16.67/100=200.04
1200- 200.04= 1000 – the approximation due to the round off- If we use 16.66666666666667 we will get the exactly 200.
Percentage Increased/ Reduced BY and Percentage Increased/ Reduced TO:
If a quantity is reduced by x% then result will (100-x)% of orginal, and if a quantity is reduced to x%, then the new value is x% of original value.
By represent difference and to represents the final value.
Ex: if a rate of product is reduced by 30%, then the new rate will be 70% of original, and if the rate of the product is reduced to 30%, then new rate will be 30% of original.
Percentage in POPULATIONS:
If the original population of region is A, and annual growth is x%. Then population after R years is \(A(1+x/100)^R\).
Increase in Population –\(A[(1+x/100)^R-1]\)
If the original population of region is A, and decrease in population is x%. Then population after R years is \(A(1-x/100)^R\).
Decrease in Population- \(A[1-(1+x/100)^R]\).
If a value of a number is first increased by R% and then decreased by R%, the net change is always a decrease or loss in original value.
Hence, % Loss or decrease = \((R/10)^2%.\)
Other Important Notes:
If a value R is increased by x% to S, and S is again decreased to R by y%, Then x is always greater than y (Positive values only).
If a value R is decreased by x% to S, and S is again increased to R by y%, then x is always less than y.
If a value P is increased by x% then by y% and then by z%, the final value will be same even if we reverse the order of x,y,z. I.e., P is increased by z% first, then by y% and then by x%. (Same for the decrease)- Successive increase or decrease in value.
Similarly if value P is increased by X% then by Y% and then decreased by Z%. the final value will be same when P is decreased by Z% first, then increased by Y%, and then by X%.
If there is an increase of x/y in any value A, then the increased value will be \(A (1+x/y)\).
If there is a decrease of x/y in any value A, then the increased value will be \(A (1-x/y)\).
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16 Jun 2024, 10:37
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Though it might be overkill to memorize it, I thought this could help save time for a lot of Data Insights section questions.
Let us take original number as 100.
10% increase --> 110. To get back to original number, percent decrease would be 9.09%
20% increase --> 120. To get back to original number, percent decrease would be 16.67%
30% increase --> 130. To get back to original number, percent decrease would be 23.08%
40% increase --> 140. To get back to original number, percent decrease would be 28.57%
50% increase --> 150. To get back to original number, percent decrease would be 33.33%
60% increase --> 160. To get back to original number, percent decrease would be 37.50%
70% increase --> 170. To get back to original number, percent decrease would be 41.18%
80% increase --> 180. To get back to original number, percent decrease would be 44.44%
90% increase --> 190. To get back to original number, percent decrease would be 47.37%
100% increase --> 200. To get back to original number, percent decrease would be 50%
Let us take original number as 100.
10% increase --> 110. To get back to original number, percent decrease would be 9.09%
20% increase --> 120. To get back to original number, percent decrease would be 16.67%
30% increase --> 130. To get back to original number, percent decrease would be 23.08%
40% increase --> 140. To get back to original number, percent decrease would be 28.57%
50% increase --> 150. To get back to original number, percent decrease would be 33.33%
60% increase --> 160. To get back to original number, percent decrease would be 37.50%
70% increase --> 170. To get back to original number, percent decrease would be 41.18%
80% increase --> 180. To get back to original number, percent decrease would be 44.44%
90% increase --> 190. To get back to original number, percent decrease would be 47.37%
100% increase --> 200. To get back to original number, percent decrease would be 50%
Attachments
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15 Mar 2026, 23:21
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