Wed May 11, 2011 By:


Expert Reply
Wed May 11, 2011
We know that when the resistance are connected in series and by question we get
When connected in parallel, by question  we get
From equation 1 and 2 we get two values of  and that is
let us take
Then from equation 1 we get
R+r=90, R=90-r, putting this value in equation 2 we get
when r is 60 ohms then R is 30 ohms and when r is 30 ohms then R is 60 ohms.
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