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The radioisotope radon-222 has a half life of 3.8 days. How much of a 73.9 g sample of radon-222 would be left after approximately 23 days?
We have
73.9 * ( 1/2)^ ( t / 3.8) where t is the number of days...so....
73.9 * (1/2) ^ (23/ 3.8) ≈ 1.11 g
+4116 
