The selling price is given by:
\[ S.P. = C.P. \times \left(1 + \frac{23}{100} \right) \]
Substituting the values:
\[ S.P. = 300 \times 1.23 = 369 \]
The shopkeeper offers a discount on the marked price, so:
\[ S.P. = M.P. \times \left(1 - \frac{x}{100} \right) \]
Substituting the values:
\[ 450 \times \left(1 - \frac{x}{100} \right) = 369 \]
Dividing both sides by 450:
\[ 1 - \frac{x}{100} = \frac{369}{450} \]
\[ 1 - \frac{x}{100} = 0.82 \]
Solving for \( x \):
\[ \frac{x}{100} = 1 - 0.82 = 0.18 \]
\[ x = 18 \]
Thus, the discount percentage is 18% (Option C).
An electricity utility company charges ₹7 per kWh. If a 40-watt desk light is left on for 10 hours each night for 180 days, what would be the cost of energy consumption? If the desk light is on for 2 more hours each night for the 180 days, what would be the percentage-increase in the cost of energy consumption?