.
A cup of coffee contains 130 milligrams of caffeine.
If caffeine is eliminated from the body at a rate of 11% per hour,
how long will it take for 90% of this caffeine to be eliminated from a person's body
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The decay equation is
M(t) = = .
To solve, divide both sides by 130
0.1 =
and take logarithm base 10 of both sides. We get then
log(0.1) = t*log(0.89)
and find
t = = 19.76 hours. ANSWER
CHECK. The remaining mass is M(19.76) = = 13.9984 milligrams,
which is a good precision, comparing with 13 milligrams.
Solved.