b
(b)If a motor of \(12 HP\) works for \(10\)  days at the rate of \(8 hr/day\)  then energy consumption = power \(×\) time =

\(12 \times 746\frac{J}{{\sec }} \times (80 \times 60 \times 60)\;\sec \)

\( = 12 \times 746 \times 80 \times 60 \times 60\;J= 2.5 × 10^9 J\)

Rate of energy = \(50\frac{{paisa}}{{kWh}}\)

i.e. \(3.6 \times {10^6}J\) energy cost \(0.5 Rs\) 

So \(2.5 × 10^9\) \(J\) 

energy cost = \(\frac{{2.5 \times {{10}^9}}}{{2 \times 3.6 \times {{10}^6}}} = 358\;Rs\)