Find the percentage increase in R.

chijioke

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Here is an example and solution?IMG_20230501_011822.jpg
I am now asking why should [math]P_1[/math] be divided by P to obtain percentage increase in P? As inIMG_20230430_165421.jpg Can somebody please explain that?
I came across a problem like that below. I am only interested in c part of the problem.
IMG_20230430_155827.jpg
Here is my solution. I followed the example I showed:
The relationship between E,R and [math]d^2[/math] is [math]E=\frac{4r}{d^2}[/math]When E and d is not increased by 3% R is given as [math]R=\frac{Ed^2}{4}[/math]When E and d is increased by 3% R changes to [math]R_1[/math][math]\rightarrow[/math] [math]R_1=\frac{E{103}^3×d^2}{{103}^3×4}[/math]Dividing
[math]R_1[/math] by R we have
[math]\frac{R_1}{R}=\frac{\cancel{E}{103}^3×\cancel{d^2}×\cancel{4}}{{100}^3×\cancel{4}×\cancel{E}\cancel{d^2}}[/math]
[math]\frac{R_1}{R}=\frac{1092727}{1000000}[/math][math]R_1=\left(1+\frac{93}{100}\right)R[/math][math]\therefore[/math] The percentage increase in R is 9.3%
But again I am asking why must I divide [math]R_1 by R[/math] as in
[math]\frac{R_1}{R}=\frac{\cancel{E}{103}^3×\cancel{d^2}×\cancel{4}}{{100}^3×\cancel{4}×\cancel{E}\cancel{d^2}}[/math] to obtain percentage increase in R?
 
I am now asking why should P1P_1P1 be divided by P to obtain percentage increase in P? As in
Why not ?:)
More seriously, if something changed from [imath]P[/imath] to [imath]P_1[/imath] how do you calculate the increase in percents?
 
I added [math]\frac{15}{200}×100[/math] That is 7.5%
So what you've done is
[math]\frac{15}{200} \times 100 = \frac{215-200}{200} \times 100 = \left (\frac{215}{200}-1\right) \times 100[/math]
In this case [imath]P = 200, P_1 = 215[/imath] and [math]\frac{P_1}{P} = \frac{215}{200} = 1.15 = 1 + 0.15 = 1 + 15\%[/math]
Does this make it any clearer?
 
So what you've done is
[math]\frac{15}{200} \times 100 = \frac{215-200}{200} \times 100 = \left (\frac{215}{200}-1\right) \times 100[/math]
In this case [imath]P = 200, P_1 = 215[/imath] and [math]\frac{P_1}{P} = \frac{215}{200} = 1.15 = 1 + 0.15 = 1 + 15\%[/math]
Does this make it any clearer?
Very clear now.
 
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