math with application
posted by liv .
If 12 % of a radioactive substance decays in 7 hours, what is the halflife of the substance?
Carry out all calculations exactly, then round the final answer to three decimal places.
The half life is what hours?

math with application 
bobpursley
an interesting thought, carrying out log calculations exactly. Would require an infinite amount time adding up an infinite series.
But more practical, not exact, but using approximations from ones calculator.. if .12 decays,then .88 remains..
.88=e^(t*ln(.5)/th)
t=7hrs, solve for th
take ln of each side
ln (.88)=ln(.5)*7 / th
thalflife= 7(ln(.5)/ln.88
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