Question

If a 20 W bulb and a 100 W fan are used for 5 and 15 hours a day respectively, then the electrical energy consumed in a period of 30 days is:

• A. 72 kWh
• B. 48 kWh
• C. 36 kWh
• D. 4.5 kWh

Hint:

Convert W·h to kWh by dividing by 1000.
Calculate separately for each appliance and sum.
Check time units (hours) and power (W).

Answer 1

The Correct Option is B

• Energy consumed: $E = P \cdot t$.
• Bulb: $E_1 = 20\ \text{W} \cdot 5\ \text{h/day} \cdot 30\ \text{days} = 3000\ \text{Wh} = 3\ \text{kWh}$.
• Fan: $E_2 = 100\ \text{W} \cdot 15\ \text{h/day} \cdot 30\ \text{days} = 45000\ \text{Wh} = 45\ \text{kWh}$.
• Total $E = E_1 + E_2 = 3 + 45 = 48\ \text{kWh}$.
• Hence, correct answer: 48 kWh.