Praxis Core Academic Skills for Educators: Mathematics (5733)Algebra and FunctionsMedium
A biologist is tracking the number of cells in a petri dish. The number of cells doubles every 20 minutes. If the initial number of cells was 100, how many cells will there be after 1 hour?
- A200
- B800
- C1600
- D400
Show answer & explanationAnswer & explanation
Correct answer: B. 800
Since the cells double every 20 minutes, in 1 hour (60 minutes) there will be 60/20 = 3 doubling periods. Starting with 100 cells, after 1 period (20 min) it's 200, after 2 periods (40 min) it's 400, and after 3 periods (60 min) it's 800.
Why the other options are wrong
- A. Calculated the population after only one doubling period.
- C. Incorrectly calculated the number of doubling periods or applied the factor too many times.
- D. Calculated the population after only two doubling periods.
Exponential Growth (Specific Period)
Modeling growth where a quantity increases by a constant factor over a fixed time interval.
- Involves a base that is the growth factor (e.g., 2 for doubling).
- The exponent is the number of growth periods.
- Time units must be consistent between the growth period and total time.
Memory trick: Start, factor, and period count.