Year 12 maths · A.1 · Exponential Models
Exponential growth and decay
Count the doublings or half-lives, then multiply or divide by 2 that many times.
See worked examples
A 1,600 mg sample has a half-life of 6 days. How much is left after 30 days?
Answer: 50 mg
A bacteria culture starts with 290 cells and doubles every 4 hours. How many cells are there after 16 hours?
Answer: 4,640
A bacteria culture starts with 20 cells and doubles every 5 hours. How many cells are there after 10 hours?
Answer: 80
Tip: Count the doublings or half-lives, then multiply or divide by 2 that many times.
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