Question

The total resistance in the parallel combination of three resistances $9\Omega ,7\Omega$ and $5\Omega$ is?

• A. $1.22\Omega$
• B. $2.20\Omega$
• C. $4.22\Omega$
• D. $2.02\Omega$

Answer 1

The correct option is B $2.20\Omega$

$\frac{1}{R}=\frac{1}{9}+\frac{1}{7}+\frac{1}{5}=\frac{35+45+63}{315}=\frac{143}{315}{\Omega }^{-1}R=\frac{315}{143}\Omega =2.20\Omega$