### Video Transcript

The number of bacteria in a laboratory quadruples every hour. There were initially
200 bacteria. Write an expression for ๐ต of ๐ก, the number of bacteria ๐ก hours after the
initial movement.

What is our question asking us to do? They want us to write an expression to help us calculate how many bacteria
would grow compared to the hours that have passed. The number of bacteria in the laboratory quadruples every hour. Quadruples would mean itโs multiplied by a factor of four. Letโs make a chart.

On hour zero before we started, there were 200 bacteria in the lab. But that number quadrupled by the first hour. That means itโs multiplied by a
factor of four. 200 times four equals 800. And by the second hour, there were 3200 bacteria.

How would we write an expression to show this? We have our 200 that we started with. In the first hour, our 200 is multiplied by four. Another way to say that is four to the first power. In our second hour, the 200 is multiplied by four and then by four again, or by
four squared. We could say 200 times four squared. Our exponent here will be the time in hours that the bacteria is growing. We could write 200 times four to the ๐ก power. This tells us to take the number of hours that the bacteria is in a lab, four to
that power times 200 will equal the total number of bacterias.

Our expression for this is 200 times four to the ๐ก power.