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Let Q represent a mass of radioactive radium (226 Ra) , in grams, whose half-life is 1620 years. The quality of radium resent after t years is given by Q = 25 ( 2 ) 1620 . - - - Determine the initial quantity (when t = 0). , - grams Determine the quantity present after 1000 years. , grams :: 13.60 :: 16.30 :: 18.40 : 20 8: 25 :: 1000 :: 1620