Practice question · Estimate
A quantity doubles every 10 hours. Without a calculator, estimate how many hours it takes to grow 8-fold.
Estimate on a scale from 0 h (0) to 60 h (60).
Hints
- Write 8 as a power of 2.
- : three consecutive doublings.
Show the answer
30 (answers within ±2 count)
Why
Three doublings, 30 hours. Thinking in doublings turns exponentials into counting, which is how epidemiologists and bankers estimate at speed (and why the "rule of 70" works).
Practise Differential models in one variable
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