Note: a radioactive decay constant is always negative.
time = [natural log(ending amount / beginning amount)] / k
time = ln (20 / 24) / -.00011
time = ln (5/6) / -.00011
time = -.018232155683 / -.00011
time = <span> <span> <span> 165.7468698455 </span> </span> </span>
time = <span> <span> <span> 165.75 years
</span></span></span>
time = [natural log(ending amount / beginning amount)] / k
time = ln (20 / 24) / -.00011
time = ln (5/6) / -.00011
time = -.018232155683 / -.00011
time = <span> <span> <span> 165.7468698455 </span> </span> </span>
time = <span> <span> <span> 165.75 years
</span></span></span>