Answer: 11
Explanation:
Exponential Functions:
y=ab^x
y=ab
x
a=\text{starting value = }550
a=starting value = 550
r=\text{rate = }18.8\% = 0.188
r=rate = 18.8%=0.188
\text{Exponential Decay:}
Exponential Decay:
b=1-r=1-0.188=0.812
b=1−r=1−0.188=0.812
\text{Write Exponential Function:}
Write Exponential Function:
y=550(0.812)^x
y=550(0.812)
x
Put it all together
\text{Plug in y-value:}
Plug in y-value:
60=550(0.812)^x
60=550(0.812)
x
\frac{60}{550}=\frac{550(0.812)^x}{550}
550
60
=
550
550(0.812)
x
Divide both sides by 550
0.109091=0.812^x
0.109091=0.812
x
\log 0.109091=\log 0.812^x
log0.109091=log0.812
x
Take the log of both sides
\log 0.109091=x\log 0.812
log0.109091=xlog0.812
use power rule to bring x to the front
\frac{\log 0.109091}{\log 0.812}=\frac{x\log 0.812}{\log 0.812}
log0.812
log0.109091
=
log0.812
xlog0.812
Divide both sides by log(0.812)
10.638757=x
10.638757=x
x\approx 11
x≈11