Question

the graph represents the function where electricity usage in kilowatts per hour of a clock radio varies directly with the number of days it is plugged into the wall current.

which is a reasonable estimate of the constant of variation?

0.25 kwh per day
0.50 kwh per day
2.40 kwh per day
4.00 kwh per day

Explanation:

Identify the relationship

Using the Direct Variation knowledge point

$$ y = kx $$

where \(y\) represents the electricity usage in kilowatt-hours (kWh), \(x\) represents the number of days, and \(k\) is the constant of variation.

Read coordinates from the graph

Using the Constant of Variation knowledge point

$$
LATEXBLOCK0
$$

Calculate the constant of variation

Using the Constant of Variation knowledge point

$$ k = \frac{y}{x} = \frac{1.0\text{ kWh}}{4\text{ days}} = 0.25\text{ kWh per day} $$

Answer:

• 0.25 kWh per day (Correct answer)
• 0.50 kWh per day
• 2.40 kWh per day
• 4.00 kWh per day