A seedling measured 2 cm at the end of week 1 and 8 cm at the end of week 3. What is the mean growth rate of the seedling over this period?

Mean growth rate is calculated as (final length − initial length) ÷ time taken. Here, (8 − 2) ÷ (3 − 1) = 6 ÷ 2 = 3 cm per week. Option A (2 cm/week) is a common error from dividing by 3 weeks total instead of the 2-week interval. Option C (4 cm/week) results from dividing the total change by 1.5, and Option D (6 cm/week) is simply the total change without dividing by time.