Homework Help: Math with science

Posted by Liz on Sunday, July 27, 2008 at 12:39pm.

Radioactive iodine treatment is so successful at treating hyperthyroidism that it has virtually replaced thyroid surgery. To the nearest full day, determine how long it will take for 400 millicuries of I-131, which has a half-life of 8 days, to decay to 3.125 millicuries.

56 days,
7 days,
128 days,
or
8 days

which one is it?

Math with science - drwls, Sunday, July 27, 2008 at 12:52pm
3.125/400 = (1/2)^(t/8)
(if t is in days)
7.8125*10^-3 = (1/2)^(t/8)

t/8 = Log(7.8125*19^-3)/Log(1/2)
= 7
t = 56 days
- Math with science - Liz, Sunday, July 27, 2008 at 1:24pm
  thank you so much!!

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