Bacteria multiply at a rate proportional to the number present. If the original number N double in 3 hours, the number of the bacteria will be 4N is (in hours).

Explanation

To solve the problem where bacteria multiply at a rate proportional to the number present, we can follow these steps:

### Step 1: Set up the differential equation
Given that the rate of growth of bacteria is proportional to the number present, we can express this mathematically as:
\[ \frac{dN}{dt} = \lambda N \]
where \( \lambda \) is a constant.
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