An element has a half-life of 2.5 days. if it begins with 100 atoms, how many will be left after 5 days?

25

Explanation:

Half life equation is:

A = A₀ (½)^(t / T)

where A is the final amount, A₀ is the initial amount, t is time, and T is the half life.

Given that A₀ = 100, t = 5, and T = 2.5:

A = 100 (½)^(5 / 2.5)

A = 100 (½)^2

A = 100 (¼)

A = 25

There will be 25 atoms left.

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