Question

The equivalent resistance of the network shown across the point A and O is R and the resistance of each branch of the octagon is r. Find the value of $\frac{210R}{47r}$

• A. 5
• B. 3
• C. 2
• D. 4

Answer 1

The correct option is C 2

see image 1
$V_C=V_C^{{}^{\prime }},V_D=V_D^{{}^{\prime }}$
On folding (see image 2)
$R=\frac{47}{105}r$
So, $\frac{210}{47}\frac{R}{r}=2$