
Mark M. answered 05/28/15
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Mathematics Teacher - NCLB Highly Qualified
at = a1(2)t/h, where a1 = initial amount, h = half life, t = time elapsed
100000 = 5(2)t/3
20000 = (2)t/3
ln 20000 = (t/3) ln 2
9.903 ≈ (t/3) ln 2
29.710 ≈ t ln 2
29.710 ≈ 0.931t
31.91 ≈ t