ATI TEAS (Test of Essential Academic Skills) Version 7MathematicsHard
A researcher is studying a new cell culture. The initial count was 300 cells. After 4 hours, the count was 1200 cells. Assuming a constant growth rate, what is the doubling time of this cell culture?
- A1.5 hours
- B1 hour
- C2 hours
- D2.5 hours
Show answer & explanationAnswer & explanation
Correct answer: C. 2 hours
The cell count increased from 300 to 1200, which is a factor of 4 (1200/300 = 4). Since 4 = 2^2, the culture doubled twice during the 4-hour period. Therefore, the doubling time is 4 hours / 2 doublings = 2 hours per doubling.
Why the other options are wrong
- A. This would mean 4 hours / 1.5 doublings = 2.66 doublings, which is not an integer factor.
- B. This would mean 4 doublings in 4 hours, resulting in 300 * 2^4 = 4800 cells.
- D. This would mean less than 2 doublings in 4 hours, resulting in less than 1200 cells.
Doubling Time (Exponential Growth)
The period required for a quantity to double in size or value, assuming a constant rate of exponential growth.
- Applies to populations growing exponentially.
- Calculated by determining how many doublings occurred over a given time.
- Often used in microbiology and finance.
Memory trick: How many 'times two' to reach the end, then divide the time, my friend!