An electric iron of 1100 W is operated for 2 hours daily through April at a tariff of Rs 5 per unit. What is the monthly electricity cost?

1. Daily energy: $1100\ \text{W} \times 2\ \text{h} = 2200\ \text{Wh} = 2.2$ kWh = 2.2 units. 2. April has 30 days, so monthly energy $= 2.2 \times 30 = 66$ units. 3. Cost $= 66 \times \text{Rs } 5 = \text{Rs } 330$. 4. The option Rs 165 uses 33 units; that wrongly takes 0.5 h or halves the daily run time. 5. The option Rs 660 assumes a 31-day month doubled, or 4.4 units/day; April has 30 days and the iron runs 2 h, giving 66 units. _Source: Balbharati (Maharashtra Board) Class 10 Science & Technology, Ch 4 "Effects of Electric Current", p.70_