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**proportionality help needed please**

stuck on a proportionality problem...

1) the pressure exerted by a fluid in a pipe varies inversely as the sixth power of the diameter. what is the multiplicative change (delta X_m) and percentage change (delta X%) in the pressure is the diameter of the pipe decreases by 20%?

[tex]p\propto \frac{1}{d^6}[/tex]

[tex]\frac{p_2}{p_1}=\frac{1}{0.2^6}[/tex]

[tex]\frac{p_2}{p_1}=15625[/tex]

therefore

[tex]\frac{15625}{1}\equiv \frac{1}{0.2^6}[/tex]

so

[tex]\Delta X_m=15625[/tex]

and

[tex]\Delta X_m -1 = \Delta X_{relative}[/tex]

and

[tex]\Delta X_{rel.} * 100 = Delta X_%[/tex]

so

[tex]15625-1=15624*100=\Delta X_%[/tex]

[tex]\Delta X_% = 1.5624 * 10^6[/tex]?

i must of done something wrong...any help appreciated