How can I solve this problem: "The half-life of element X is 5 days. If we have 5g of X initially, what is the mass of X after 5 days, 20 days and 40 days"?

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How can I solve this problem: "The half-life of element X is 5 days. If we have 5g of X initially, what is the mass of X after 5 days, 20 days and 40 days"?

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Dr. Md Rushad Rahman · Answer 1 · Jan 23, 2016 07:12:42

After 5 days, there will be 2.5 g remaining. Every 5 days we divide by 2. Therefore after 10 days we have 1.25, after 15 we have 0.625, after 20 we have 0.3125 grams. You can do the same thing for 40 days. Heres a formula which is easier to use: A(t) = Ainitial*(1/2)^(t/k), where k is the half life, in this case 5, and t is the duration you are calculating for.

How can I solve this problem: "The half-life of element X is 5 days. If we have 5g of X initially, what is the mass of X after 5 days, 20 days and 40 days"?

1 Answers