SOLUTION: Strontium 90 decays at a constant rate of 2.44% per year. Therefore, the equation for the amount P of strontium 90 after t years is P =P0e -0.244t. How long will it take for 15 gra

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Question 1055032: Strontium 90 decays at a constant rate of 2.44% per year. Therefore, the equation for the amount P of strontium 90 after t years is P =P0e -0.244t. How long will it take for 15 grams of strontium to decay to 5 grams? Round answer to 2 decimal places.
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
+5+=+15%2Ae%5E%28+-.244t+%29+
+1%2F3+=+e%5E%28-.244t+%29+
Take the natural log of both sides
+ln%281%2F3%29+=+ln%28+e%5E%28-.244t+%29%29+
+-1.0986123+=+-.244t+
+t+=+4.5025+
It will take 4.50 yrs
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check:
+5+=+15%2Ae%5E%28+-.244t+%29+
+5+=+15%2Ae%5E%28+-.244%2A4.5025+%29+
+5+=+15%2Ae%5E%28+-1.09861+%29+
+5+=+15%2A.333334+
+5+=+5.00001+
close enough