(a) Initially there is one bacteria.

After 15 minutes, there will be 2 bacteria.

Thus, after 30 minutes there will be 4 bacteria, after 45 minutes there will be 8 bacteria and after 1 hour there will be 16 bacteria.

Therefore, in terms of hours , .

Find the common ratio .

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For an explicit formula, substitute  and in the term formula.

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Write an explicit formula for number of bacteria present after hours.

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(b) Find .

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Substitute and in the term formula.

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Number of bacteria present 4 hours later is .

(a) .

(b) Number of bacteria present 4 hours later is .