# Thread: Exponential Functions - Check if this is right?

1. ## Exponential Functions - Check if this is right?

In 1980 a town's population was 100,000. In 2007 it was 220,000. Estimate what the population will be in 2020 if its growth is exponential.

y=ka^x
220,000=100,000a^27
2.2=a^27
a = 1.0296

y=100,000(1.0296)^40
y=321,174.72

The population would be roughly 321,174.

Thats what I got for my answer, but the in the book its saying that y=100,000(1.026)^t is the equation that you would use and that 279,000 would be the population in 2020. Did I do something wrong with the years or is the answer in the back wrong?

2. Originally Posted by peekay
In 1980 a town's population was 100,000. In 2007 it was 220,000. Estimate what the population will be in 2020 if its growth is exponential.

y=ka^x
220,000=100,000a^27
2.2=a^27
a = 1.0296

y=100,000(1.0296)^40
y=321,174.72

The population would be roughly 321,174.

Thats what I got for my answer, but the in the book its saying that y=100,000(1.026)^t is the equation that you would use and that 279,000 would be the population in 2020. Did I do something wrong with the years or is the answer in the back wrong?
Your work looks fine. I checked with a graphing device as well.

3. Thank you, appreciate your time.