A line graph shows temperature rising from 10°C to 20°C over 5 hours. What is the average rate of change per hour?

• A. 4°C per hour
• B. 1°C per hour
• C. 2°C per hour
• D. 3°C per hour

Answer: (C)

The main idea is rate of change: how much the temperature changes per unit of time. For a line, the average rate equals the slope, which is (final minus initial) divided by the time interval. Here the temperature rises from 10°C to 20°C, a rise of 10°C, over 5 hours. So 10°C ÷ 5 hours = 2°C per hour. That means the temperature increases, on average, by 2 degrees each hour. The other options would lead to different final temperatures after 5 hours (4°C per hour would reach 30°C, 1°C per hour would reach 15°C, and 3°C per hour would reach 25°C), which doesn’t match the given data.