Question

The number of cell phones, y(in thousands), from 1985 to 1995 can be modeled using the equation y=0.432(1.55)^x, where x is the number of years after 1985. In what year were there approximately 6 thousand cell phones?

A 1989
B 1991
C 1993
D 1995

Answer 1

is it
\[y=0.43(1.55)^x\]?

Answer 2

that's the formula

Answer 3

ok then set
\[6=.432(1.55)^x\] and solve for \(x\)

Answer 4

I think you have to put the answer choices into the y and then see which one fits

Answer 5

first step is to divide by \(.432\)

Answer 6

which is 13.88888888888888888

Answer 7

you get
\[\frac{6}{.432}=13.8=(1.55)^x\] then use the change of base formula to get
\[x=\frac{\ln(13.8)}{\ln(1.55)}\] and then a calculator

Answer 8

so 13.8/1.55?

Answer 9

if this looks like a mystery to you, then you can just plug in the various numbers for your answer and see which one works

Answer 10

do you know about logarithms?

Answer 11

no it is not what you wrote, it is the one i wrote that uses logs
if you do not know about logs then try various numbers to see which one gives you the closest to 6
you should see that \(x=6\) is the closest

Answer 12

six years after 1985 is 1991 for the final answer