Question 1156187
1/R=1/80+1/100; multiply by LCD of 400R and 400=5R+4R=9R, so R=400/9=44.44 ohms

R^(-1)=(R1)^(-1)+R2^(-1)
-1/R^2 dR/ds=-1/R1^2 dR1/ds-1/R2^2 dR2/ds
-1/1975.31 dR/ds=-1/6400*0.3-1/10000*0.2
so 
-0.000506 dR/ds=-0.0000469-0.00002=-0.0000669.  Change all signs and divide by 0.000506
dR/ds=0.132 ohms/sec.