Let the salary of the officer be Rs \(x\).
10% is deducted as house rent, so he is left with 90% of his salary:
\(\text{Remaining salary} = 0.9x\)
He spends 15% of the remaining salary on children's education, so he is left with 85% of this:
\(\text{After education expenditure} = 0.85 \times 0.9x = 0.765x\)
He spends 10% of the balance on clothes, so he is left with 90% of this:
\(\text{After clothes expenditure} = 0.9 \times 0.765x = 0.6885x\)
After all these expenditures, he is left with Rs 1377:
\(0.6885x = 1377\)
Solving for \(x\)
\(x = \frac{1377}{0.6885} = 2000\)
Thus, the officer's salary is Rs \(2000\).
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?