## 271. Math Puzzle 12/87

How long can a 60 W incandescent bulb burn until 1 kWh is consumed? What are the energy costs for this?
A 60 W incandescent lamp can burn for $x$ hours, where

$$
60 \mathrm{~W} \cdot x=1000 \mathrm{Wh}=1 \mathrm{kWh} \quad, \quad x=16.67 \mathrm{~h}=16 \mathrm{~h} 40 \mathrm{~min}
$$

The lamp can burn for 16 hours and 40 minutes. The cost of $1 \mathrm{kWh}$ of household energy in our state is only 8 pennies!