(1/2)^(10/k)=0.8=4/5(12)10k=0.8=45. Now taking log on both sides
(10/k)log(1/2)=log(4/5)(10k)log(12)=log(45) or
(10/k)=log(4/5)/log(1/2)(10k)=log(45)log(12) or
10=k*log(4/5)/log(1/2)10=k⋅log(45)log(12) or
k=10/(log(4/5)/log(1/2))k=10log(45)log(12) or
k=10*log(1/2)/log(4/5)=10*(-0.3010)/(-0.09691)k=10⋅log(12)log(45)=10⋅−0.3010−0.09691
or k=31.06k=31.06