Advanced Math practice question

Answer: 10

15 years is three half-lives (15 / 5 = 3), so the mass halves three times: 80 → 40 → 20 → 10 grams. (As a formula: 80 · (1/2)³ = 10.)

Common wrong answers

If you answered 5

5 would be four half-lives, 20 years. 15 / 5 = 3 halvings, giving 10.

If you answered 20

20 is after two half-lives, 10 years. One more halving is needed for 15 years.

If you answered 40

40 is after ONE half-life, 5 years. 15 years is three of them.

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