When exposed to sunlight, the # of bacteria in a culture decreases exponentially at the rate of 10% per hour. What is the best approximation for the number of hours required for the initial # of bacteria to decrease by 50%.

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- Jun 6th 2008, 09:38 PMcityismineexponential growth/decay word problem
When exposed to sunlight, the # of bacteria in a culture decreases exponentially at the rate of 10% per hour. What is the best approximation for the number of hours required for the initial # of bacteria to decrease by 50%.

- Jun 6th 2008, 10:54 PMearboth
Let A(0) denote the initial amount of bacteria and A(t) the amount of bacteria after t hours of exposion to sun light.

After 1 h there remains 90% of the bacteria. After t hours remains of the bacteria.

You know that

Use the equation

plug in the values you know and solve for t.

I've got t is roughly 6h 35 min - Jun 6th 2008, 10:54 PMTKHunny
Learning to translate is the point, here.

"# of bacteria in a culture"

Define this. B(t) = # of bacteria in a culture - at time t in hours.

"decreases exponentially"

A clue about

"decreases exponentially at the rate of 10% per hour."

A clue about the parameter:

"number of hours required for the initial # of bacteria to decrease by 50%."

B(x) = -- Solve for x.