A 12 HP motor has to be operated 8 hours/day. How much will it cost at the rate of 50 paisa/kWh in 10 days (in Rs)

If a motor of 12 HP works for 10 days at the rate of 8 hr/day then energy consumption = power × time 
$=12\times 746\frac{\mathrm{J}}{\sec }\times (80\times 60\times 60)\sec$
$=12\times 746\times 80\times 60\times 60\mathrm{J}$ = 2.5 × 10⁹ J
Rate of energy = $50\frac{\mathrm{paisa}}{\mathrm{kWh}}$
i.e. $3.6\times {10}^6\mathrm{J}$ energy cost 0.5 Rs
So 2.5 × 10⁹ J energy cost = $\frac{2.5\times {10}^9}{2\times 3.6\times {10}^6}=348\mathrm{Rs}$