How is the rate of change between two data points calculated?

• A. (value at end - value at start) / time between measurements.
• B. (value at start - value at end) / time between measurements.
• C. (value at end + value at start) / time between measurements.
• D. (value at end - value at start) * time between measurements.

Answer: (A)

Rate of change between two data points shows how much the value changes per unit of time. The standard way is to take the difference in value from the end point to the start point and divide by the time elapsed between measurements. So it is (end value minus start value) divided by the time between measurements. This yields a rate with units like units per year (or per second, etc.).

For example, if you start at 100 and end at 120 over 2 years, the rate is (120 − 100) / 2 = 10 units per year.

The other options aren’t correct because they either reverse the subtraction (giving a negative rate when the value increases), add the values (not a rate at all), or multiply by time (which would not express rate per unit time).