Practice!

Sample Problem

A petri dish starts off with 10 bacteria, and the bacteria population doubles every hour. How many bacteria are in the petri dish after 8 hours?

bacteria

Solution

y =  a bx     a: start value, b: multiplier. x: number of intervals.

We first write an exponential model for this situation, then plug in

a = 10, b = 2, x = 8

y = 10 × 2x

y = 10 × 28

y = 10 × 256

y = 2560 bacteria