It\'s possible to estimate the percentage of fat in the body by measuring the re

Question

It's possible to estimate the percentage of fat in the body by measuring the resistance of the upper leg rather than the upper arm; the calculation is similar. A person's leg meas-ures 40 cm between the knee and the hip, with an average leg diameter (ignoring bone and other poorly conducting tissue) of 12 cm . A potential difference of 0.74 V causes a current of 1.6 mA .

What are the fractions of muscle and fat in the leg?

Express your answer using two significant figures separated by a comma.

I've gotten fm as 96 and ff as 4 and it says its very close but incorrect.

Explanation / Answer

We know that the total resistance, Rtot=Rf||Rm

1/Rtot=I/V=1/Rf+1/Rm=fA/pfL+(1-f)A/pmL

=Apmf+pf(1-f)/(Lpfpm)

=A((pm-pf)f+pf)/Lpfpm

So,ILpfpm/VA=(pm-pf)f+pf

=>f=ILpm/VA-1(pf/(pm-pf)

pf=25 ohm m

pm=13 ohm m

f=1.6*0.4*13/0.74*A-1*(25/12)=0.28

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