A bacteria colony doubles in size every hour. At 1:00 pm there are 10 bacteria in a petri dish. At 9:00 pm on the same day, what is the bacteria population?
Every hour, the bacteria population is multiplied by 2. At 2:00 pm, the bacteria population has doubled once and there are $10\cdot2$ bacteria. At 3:00 pm, the bacteria population has doubled twice and there are $10\cdot2\cdot2$ bacteria, etc. By 9:00 pm, the bacteria colony has doubled in size 8 times. Therefore, there are $10\cdot2\cdot2\cdot2\cdot2\cdot2\cdot2\cdot2\cdot2$ or $10\cdot2^8$ bacteria so we get  $$10\cdot2^8=10\cdot256=\boxed{2560}\mbox{ bacteria.}$$