Jawabanmu

2014-01-11T17:18:00+07:00
Massa sisa = massa awal x  \frac{1}{2} ^{ \frac{t}{20} }
1/8 massa awal = massa awal x  \frac{1}{2} ^{ \frac{t}{20} }
1/8 =  \frac{1}{2} ^{ \frac{t}{20} }
 \frac{1}{2}^3 = \frac{1}{2} ^{ \frac{t}{20} }\\
3= \frac{t}{20}
t=60 hari