a
Current drawn from a battery when $n$ resistors are connected in series is
$I=\frac{E}{n R+R}$ .....$(i)$
Current drawn from same battery when $n$ resistors are connected in parallel is
$10 I=\frac{E}{R / n+R}$ ......$(ii)$
On dividing eqn. $(ii)$ by $(i),$ $10=\frac{(n+1) R}{(1 / n+1) R}$
After solving the equation, $n=10$.