Question

In Millersburg, the use of landlines has been declining at a rate of 10% every year. If there are 42,000 landlines this year, how many will there be in 7 years?If necessary, round your answer to the nearest whole number.

Answer 1

To calculate how many landlines will be used in 7 years you have to apply the exponential decay

`y=a(1-r)^x`

Where

a is the initial value

r is the decay rate (this value is given as a percentage, you have to use it expressed as a decimal)

x is the time interval that has passed

We know that there are 42000 landlines this year

The declining rate is 10% → expressed as a decimal value r=0.1

The time-lapse is 7 years

`\begin{gathered} y=42000(1-0.1)^7 \\ y=20088.47 \end{gathered}`

In 7 years there will be 20088.47 landlines