Physics - Current Electricity Question with Solution | TestHub

The series combination of two batteries, both of the same emf 10 V , but different internal resistance of $20\Omega$ and $5\Omega$, is connected to the parallel combination of two resistors $30\Omega$ and $\mathrm{R}\Omega$. The batteries are connected in series aiding. The voltage difference across the battery of internal resistance $20\Omega$ is zero, the value of R (in $\Omega$ ) is : $\_\_\_\_$