Exponential growth and decay by a factor

exponential growth/decay: ${ A_f = A_i (f)^{time\over period}}$

${A_f}$: final amount
${A_i}$: initial amount
${f }$ : growth/decay factor
half-time$\to f = {1\over 2}$
triple$\to f = {3}$
ten-fold$\to f = {10}$
increase by 10%$\to f = {({1 + {10\over 100}}) } { = 1.1}$
decrease by 8%$\to f = {({1 - {8\over 100}}) } { = 0.92}$
${time}$ : total time given
${period}$ : every length of time